SENDMAIL
TM
INSTALLATION AND OPERATION GUIDE
Eric Allman
Claus Assmann
Gregory Neil Shapiro
Proofpoint, Inc.
For Sendmail Version 8.18
Sendmail
TM
implements a general purpose internetwork mail routing facility under the UNIX® operating sys-
tem. It is not tied to any one transport protocol — its function may be likened to a crossbar switch, relaying mes-
sages from one domain into another. In the process, it can do a limited amount of message header editing to put the
message into a format that is appropriate for the receiving domain. All of this is done under the control of a configu-
ration file.
Due to the requirements of flexibility for
sendmail
, the configuration file can seem somewhat unapproachable.
However, there are only a few basic configurations for most sites, for which standard configuration files have been
supplied. Most other configurations can be built by adjusting an existing configuration file incrementally.
Sendmail
is based on RFC 821 (Simple Mail Transport Protocol), RFC 822 (Internet Mail Headers Format),
RFC 974 (MX routing), RFC 1123 (Internet Host Requirements), RFC 1413 (Identification server), RFC 1652
(SMTP 8BITMIME Extension), RFC 1869 (SMTP Service Extensions), RFC 1870 (SMTP SIZE Extension), RFC
1891 (SMTP Delivery Status Notifications), RFC 1892 (Multipart/Report), RFC 1893 (Enhanced Mail System Sta-
tus Codes), RFC 1894 (Delivery Status Notifications), RFC 1985 (SMTP Service Extension for Remote Message
Queue Starting), RFC 2033 (Local Message Transmission Protocol), RFC 2034 (SMTP Service Extension for Re-
turning Enhanced Error Codes), RFC 2045 (MIME), RFC 2476 (Message Submission), RFC 2487 (SMTP Service
Extension for Secure SMTP over TLS), RFC 2554 (SMTP Service Extension for Authentication), RFC 2821 (Sim-
ple Mail Transfer Protocol), RFC 2822 (Internet Message Format), RFC 2852 (Deliver By SMTP Service Exten-
sion), RFC 2920 (SMTP Service Extension for Command Pipelining), and RFC 7505 (A "Null MX" No Service Re-
source Record for Domains That Accept No Mail). However, since
sendmail
is designed to work in a wider world,
in many cases it can be configured to exceed these protocols. These cases are described herein.
Although
sendmail
is intended to run without the need for monitoring, it has a number of features that may be
used to monitor or adjust the operation under unusual circumstances. These features are described.
Section one describes how to do a basic
sendmail
installation. Section two explains the day-to-day informa-
tion you should know to maintain your mail system. If you have a relatively normal site, these two sections should
contain sufficient information for you to install
sendmail
and keep it happy. Section three has information regarding
the command line arguments. Section four describes some parameters that may be safely tweaked. Section five
contains the nitty-gritty information about the configuration file. This section is for masochists and people who must
write their own configuration file. Section six describes configuration that can be done at compile time. The appen-
dixes give a brief but detailed explanation of a number of features not described in the rest of the paper.
DISCLAIMER:
This documentation is under modification.
Sendmail is a trademark of Proofpoint, Inc. US Patent Numbers 6865671, 6986037.
Sendmail Installation and Operation Guide
SMM:08-1
Sendmail Installation and Operation Guide
SMM:08-7
1. BASIC INSTALLATION
There are two basic steps to installing
sendmail
. First, you have to compile and install the binary. If
send-
has already been ported to your operating system that should be simple. Second, you must build a run-time
configuration file. This is a file that
sendmail
reads when it starts up that describes the mailers it knows about,
how to parse addresses, how to rewrite the message header, and the settings of various options. Although the
configuration file can be quite complex, a configuration can usually be built using an M4-based configuration
language. Assuming you have the standard
sendmail
distribution, see
cf/README
for further information.
The remainder of this section will describe the installation of
sendmail
assuming you can use one of the
existing configurations and that the standard installation parameters are acceptable. All pathnames and examples
are given from the root of the
sendmail
subtree, normally
/usr/src/usr.sbin/sendmail
on 4.4BSD-based systems.
Continue with the next section if you need/want to compile
sendmail
yourself. If you have a running bi-
nary already on your system, you should probably skip to section 1.2.
1.1. Compiling Sendmail
All
sendmail
source is in the
sendmail
subdirectory. To compile sendmail, “cd” into the
sendmail
di-
rectory and type
./Build
This will leave the binary in an appropriately named subdirectory, e.g., obj.BSD-OS.2.1.i386. It works for
multiple object versions compiled out of the same directory.
1.1.1. Tweaking the Build Invocation
You can give parameters on the
Build
command. In most cases these are only used when the
obj.*
directory is first created. To restart from scratch, use
-c
. These commands include:
−L
libdirs
A list of directories to search for libraries.
−I
incdirs
A list of directories to search for include files.
−E
envar
=
value
Set an environment variable to an indicated
value
before compiling.
−c Create a new
obj.*
tree before running.
−f
siteconfig
Read the indicated site configuration file. If this parameter is not specified,
Build
includes
all
of
the files
$BUILDTOOLS/Site/site.$oscf.m4
and
$BUILDTOOLS/Site/site.config.m4
, where
$BUILDTOOLS is normally
../devtools
and $oscf is the same name as used on the
obj.*
direc-
tory. See below for a description of the site configuration file.
−S Skip auto-configuration.
Build
will avoid auto-detecting libraries if this is set. All libraries and
map definitions must be specified in the site configuration file.
Most other parameters are passed to the
make
program; for details see
$BUILDTOOLS/README
.
1.1.2. Creating a Site Configuration File
See sendmail/README for various compilation flags that can be set, and devtools/README for
details how to set them.
1.1.3. Tweaking the Makefile
Sendmail
supports two different formats for the local (on disk) version of databases, notably the
aliases
database. At least one of these should be defined if at all possible.
SMM:08-8 Sendmail Installation and Operation Guide
CDB Constant DataBase (tinycdb).
NDBM The ‘‘new DBM’’ format, available on nearly all systems around today. This was the
preferred format prior to 4.4BSD. It allows such complex things as multiple databases
and closing a currently open database.
NEWDB The Berkeley DB package. If you have this, use it. It allows long records, multiple
open databases, real in-memory caching, and so forth. You can define this in conjunc-
tion with
NDBM
; if you do, old alias databases are read, but when a new database is
created it will be in NEWDB format. As a nasty hack, if you have NEWDB, NDBM,
and NIS defined, and if the alias file name includes the substring “/yp/”,
sendmail
will
create both new and old versions of the alias file during a
newalias
command. This is
required because the Sun NIS/YP system reads the DBM version of the alias file. It’s
ugly as sin, but it works.
If neither of these are defined,
sendmail
reads the alias file into memory on every invocation. This can be
slow and should be avoided. There are also several methods for remote database access:
LDAP Lightweight Directory Access Protocol.
NIS Sun’s Network Information Services (formerly YP).
NISPLUS Sun’s NIS+ services.
NETINFO NeXT’s NetInfo service.
HESIOD Hesiod service (from Athena).
Other compilation flags are set in
conf.h
and should be predefined for you unless you are porting to a new
environment. For more options see
sendmail/README
.
1.1.4. Compilation and installation
After making the local system configuration described above, You should be able to compile and
install the system. The script “Build” is the best approach on most systems:
./Build
This will use
uname
(1) to create a custom Makefile for your environment.
If you are installing in the standard places, you should be able to install using
./Build install
This should install the binary in /usr/sbin and create links from /usr/bin/newaliases and /usr/bin/mailq to
/usr/sbin/sendmail. On most systems it will also format and install man pages. Notice: as of version 8.12
sendmail
will no longer be installed set-user-ID root by default. If you really want to use the old method,
you can specify it as target:
./Build install-set-user-id
1.2. Configuration Files
Sendmail
cannot operate without a configuration file. The configuration defines the mail delivery
mechanisms understood at this site, how to access them, how to forward email to remote mail systems, and a
number of tuning parameters. This configuration file is detailed in the later portion of this document.
The
sendmail
configuration can be daunting at first. The world is complex, and the mail configuration
reflects that. The distribution includes an m4-based configuration package that hides a lot of the complexity.
See
cf/README
for details.
Our configuration files are processed by
m4
to facilitate local customization; the directory
cf
of the
sendmail
distribution directory contains the source files. This directory contains several subdirectories:
cf Both site-dependent and site-independent descriptions of hosts. These can be literal host
names (e.g., “ucbvax.mc”) when the hosts are gateways or more general descriptions (such
Sendmail Installation and Operation Guide
SMM:08-9
as “generic-solaris2.mc” as a general description of an SMTP-connected host running So-
laris 2.x. Files ending
.mc
(‘‘M4 Configuration’’) are the input descriptions; the output is
in the corresponding
.cf
file. The general structure of these files is described below.
domain Site-dependent subdomain descriptions. These are tied to the way your organization wants
to do addressing. For example,
domain/CS.Berkeley.EDU.m4
is our description for hosts
in the CS.Berkeley.EDU subdomain. These are referenced using the
DOMAIN
m4
macro
in the
.mc
file.
feature Definitions of specific features that some particular host in your site might want. These are
referenced using the
FEATURE
m4
macro. An example feature is use_cw_file (which tells
sendmail
to read an /etc/mail/local-host-names file on startup to find the set of local
names).
hack Local hacks, referenced using the
HACK
m4
macro. Try to avoid these. The point of hav-
ing them here is to make it clear that they smell.
m4 Site-independent
m4
(1) include files that have information common to all configuration
files. This can be thought of as a “#include” directory.
mailer Definitions of mailers, referenced using the
MAILER
m4
macro. The mailer types that are
known in this distribution are fax, local, smtp, uucp, and usenet. For example, to include
support for the UUCP-based mailers, use “MAILER(uucp)”.
ostype Definitions describing various operating system environments (such as the location of sup-
port files). These are referenced using the
OSTYPE
m4
macro.
sh Shell files used by the
m4
build process. You shouldn’t hav e to mess with these.
siteconfig Local UUCP connectivity information. This directory has been supplanted by the mail-
ertable feature; any new configurations should use that feature to do UUCP (and other)
routing. The use of this directory is deprecated.
If you are in a new domain (e.g., a company), you will probably want to create a cf/domain file for
your domain. This consists primarily of relay definitions and features you want enabled site-wide: for exam-
ple, Berkeley’s domain definition defines relays for BitNET and UUCP. These are specific to Berkeley, and
should be fully-qualified internet-style domain names. Please check to make certain they are reasonable for
your domain.
Subdomains at Berkeley are also represented in the cf/domain directory. For example, the domain
CS.Berkeley.EDU is the Computer Science subdomain, EECS.Berkeley.EDU is the Electrical Engineering
and Computer Sciences subdomain, and S2K.Berkeley.EDU is the Sequoia 2000 subdomain. You will prob-
ably have to add an entry to this directory to be appropriate for your domain.
You will have to use or create
.mc
files in the
cf/cf
subdirectory for your hosts. This is detailed in the
cf/README file.
1.3. Details of Installation Files
This subsection describes the files that comprise the
sendmail
installation.
1.3.1. /usr/sbin/sendmail
The binary for
sendmail
is located in /usr/sbin
1
. It should be set-group-ID smmsp as described in
sendmail/SECURITY. For security reasons, /, /usr, and /usr/sbin should be owned by root, mode 0755
2
.
1
This is usually /usr/sbin on 4.4BSD and newer systems; many systems install it in /usr/lib. I understand it is in /usr/ucblib on System V
Release 4.
2
Some vendors ship them owned by bin; this creates a security hole that is not actually related to
sendmail
. Other important directories
that should have restrictive ownerships and permissions are /bin, /usr/bin, /etc, /etc/mail, /usr/etc, /lib, and /usr/lib.
SMM:08-10 Sendmail Installation and Operation Guide
1.3.2. /etc/mail/sendmail.cf
This is the main configuration file for
sendmail
3
. This is one of the two non-library file names
compiled into
sendmail
4
, the other is /etc/mail/submit.cf.
The configuration file is normally created using the distribution files described above. If you have
a particularly unusual system configuration you may need to create a special version. The format of this
file is detailed in later sections of this document.
1.3.3. /etc/mail/submit.cf
This is the configuration file for
sendmail
when it is used for initial mail submission, in which case
it is also called ‘‘Mail Submission Program’’ (MSP) in contrast to ‘‘Mail Transfer Agent’’ (MTA). Start-
ing with version 8.12,
sendmail
uses one of two different configuration files based on its operation mode
(or the new
−A
option). For initial mail submission, i.e., if one of the options
−bm
(default),
−bs
, or
−t
is
specified, submit.cf is used (if available), for other operations sendmail.cf is used. Details can be found
in
sendmail/SECURITY
. submit.cf is shipped with sendmail (in cf/cf/) and is installed by default. If
changes to the configuration need to be made, start with cf/cf/submit.mc and follow the instruction in
cf/README.
1.3.4. /usr/bin/newaliases
The
newaliases
command should just be a link to
sendmail
:
rm −f /usr/bin/newaliases
ln −s /usr/sbin/sendmail /usr/bin/newaliases
This can be installed in whatever search path you prefer for your system.
1.3.5. /usr/bin/hoststat
The
hoststat
command should just be a link to
sendmail
, in a fashion similar to
newaliases
. This
command lists the status of the last mail transaction with all remote hosts. The
−v
flag will prevent the
status display from being truncated. It functions only when the
HostStatusDirectory
option is set.
1.3.6. /usr/bin/purgestat
This command is also a link to
sendmail
. It flushes expired (Timeout.hoststatus) information that
is stored in the
HostStatusDirectory
tree.
1.3.7. /var/spool/mqueue
The directory
/var/spool/mqueue
should be created to hold the mail queue. This directory should
be mode 0700 and owned by root.
The actual path of this directory is defined by the
QueueDirectory
option of the
sendmail.cf
file.
To use multiple queues, supply a value ending with an asterisk. For example,
/var/spool/mqueue/qd*
will use all of the directories or symbolic links to directories beginning with ‘qd’ in
/var/spool/mqueue
as
queue directories. Do not change the queue directory structure while sendmail is running.
If these directories have subdirectories or symbolic links to directories named ‘qf’, ‘df’, and ‘xf’,
then these will be used for the different queue file types. That is, the data files are stored in the ‘df’
3
Actually, the pathname varies depending on the operating system; /etc/mail is the preferred directory. Some older systems install it in
/usr/lib/sendmail.cf
, and I’ve also seen it in
/usr/ucblib
. If you want to move this file, add -D_PATH_SENDMAILCF=\"/file/name\" to the flags
passed to the C compiler. Moving this file is not recommended: other programs and scripts know of this location.
4
The system libraries can reference other files; in particular, system library subroutines that
sendmail
calls probably reference
/etc/passwd
and
/etc/resolv.conf
.
Sendmail Installation and Operation Guide
SMM:08-11
subdirectory, the transcript files are stored in the ‘xf’ subdirectory, and all others are stored in the ‘qf’
subdirectory.
If shared memory support is compiled in,
sendmail
stores the available diskspace in a shared mem-
ory segment to make the values readily available to all children without incurring system overhead. In
this case, only the daemon updates the data; i.e., the sendmail daemon creates the shared memory seg-
ment and deletes it if it is terminated. To use this,
sendmail
must have been compiled with support for
shared memory (-DSM_CONF_SHM) and the option
SharedMemoryKey
must be set. Notice: do not
use the same key for
sendmail
invocations with different queue directories or different queue group dec-
larations. Access to shared memory is not controlled by locks, i.e., there is a race condition when data in
the shared memory is updated. However, since operation of
sendmail
does not rely on the data in the
shared memory, this does not negatively influence the behavior.
1.3.8. /var/spool/clientmqueue
The directory
/var/spool/clientmqueue
should be created to hold the mail queue. This directory
should be mode 0770 and owned by user smmsp, group smmsp.
The actual path of this directory is defined by the
QueueDirectory
option of the
submit.cf
file.
1.3.9. /var/spool/mqueue/.hoststat
This is a typical value for the
HostStatusDirectory
option, containing one file per host that this
sendmail has chatted with recently. It is normally a subdirectory of
mqueue
.
1.3.10. /etc/mail/aliases*
The system aliases are held in “/etc/mail/aliases”. A sample is given in “sendmail/aliases” which
includes some aliases which
must
be defined:
cp sendmail/aliases /etc/mail/aliases
edit /etc/mail/aliases
You should extend this file with any aliases that are apropos to your system.
Normally
sendmail
looks at a database version of the files, stored either in “/etc/mail/aliases.dir”
and “/etc/mail/aliases.pag” or “/etc/mail/aliases.db” depending on which database package you are using.
The actual path of this file is defined in the
AliasFile
option of the
sendmail.cf
file.
The permissions of the alias file and the database versions should be 0640 to prevent local denial of
service attacks as explained in the top level
README
in the sendmail distribution. If the permissions
0640 are used, be sure that only trusted users belong to the group assigned to those files. Otherwise, files
should not even be group readable.
1.3.11. /etc/rc or /etc/init.d/sendmail
It will be necessary to start up the
sendmail
daemon when your system reboots. This daemon per-
forms two functions: it listens on the SMTP socket for connections (to receive mail from a remote sys-
tem) and it processes the queue periodically to insure that mail gets delivered when hosts come up.
If necessary, add the following lines to “/etc/rc” (or “/etc/rc.local” as appropriate) in the area where
it is starting up the daemons on a BSD-base system, or on a System-V-based system in one of the startup
files, typically “/etc/init.d/sendmail”:
if [ −f /usr/sbin/sendmail −a −f /etc/mail/sendmail.cf ]; then
(cd /var/spool/mqueue; rm −f xf*)
/usr/sbin/sendmail −bd −q30m &
echo −n ’ sendmail’ >/dev/console
fi
The “cd” and “rm” commands insure that all transcript files have been removed; extraneous transcript
SMM:08-12 Sendmail Installation and Operation Guide
files may be left around if the system goes down in the middle of processing a message. The line that ac-
tually invokes
sendmail
has two flags: “−bd” causes it to listen on the SMTP port, and “−q30m” causes it
to run the queue every half hour.
Some people use a more complex startup script, removing zero length qf/hf/Qf files and df files for
which there is no qf/hf/Qf file. Note this is not advisable. For example, see Figure 1 for an example of a
complex script which does this clean up.
1.3.12. /etc/mail/helpfile
This is the help file used by the SMTP
HELP
command. It should be copied from “sendmail/help-
file”:
cp sendmail/helpfile /etc/mail/helpfile
The actual path of this file is defined in the
HelpFile
option of the
sendmail.cf
file.
1.3.13. /etc/mail/statistics
If you wish to collect statistics about your mail traffic, you should create the file “/etc/mail/statis-
tics”:
cp /dev/null /etc/mail/statistics
chmod 0600 /etc/mail/statistics
This file does not grow. It is printed with the program “mailstats/mailstats.c.” The actual path of this file
is defined in the
S
option of the
sendmail.cf
file.
1.3.14. /usr/bin/mailq
If
sendmail
is invoked as “mailq,” it will simulate the
−bp
flag (i.e.,
sendmail
will print the con-
tents of the mail queue; see below). This should be a link to /usr/sbin/sendmail.
1.3.15. sendmail.pid
sendmail
stores its current pid in the file specified by the
PidFile
option (default is _PATH_SEND-
MAILPID).
sendmail
uses
TempFileMode
(which defaults to 0600) as the permissions of that file to
prevent local denial of service attacks as explained in the top level
README
in the sendmail distribu-
tion. If the file already exists, then it might be necessary to change the permissions accordingly, e.g.,
chmod 0600 /var/run/sendmail.pid
Note that as of version 8.13, this file is unlinked when
sendmail
exits. As a result of this change, a script
such as the following, which may have worked prior to 8.13, will no longer work:
# stop & start sendmail
PIDFILE=/var/run/sendmail.pid
kill ‘head -1 $PIDFILE‘
‘tail -1 $PIDFILE‘
because it assumes that the pidfile will still exist even after killing the process to which it refers. Below
is a script which will work correctly on both newer and older versions:
# stop & start sendmail
PIDFILE=/var/run/sendmail.pid
pid=‘head -1 $PIDFILE‘
cmd=‘tail -1 $PIDFILE‘
kill $pid
$cmd
This is just an example script, it does not perform any error checks, e.g., whether the pidfile exists at all.
Sendmail Installation and Operation Guide
SMM:08-13
#!/bin/sh
# remove zero length qf/hf/Qf files
for qffile in qf* hf* Qf*
do
if [ −r $qffile ]
then
if [ ! −s $qffile ]
then
echo −n " <zero: $qffile>" > /dev/console
rm −f $qffile
fi
fi
done
# rename tf files to be qf if the qf does not exist
for tffile in tf*
do
qffile=‘echo $tffile | sed ’s/t/q/’‘
if [ −r $tffile −a ! −f $qffile ]
then
echo −n " <recovering: $tffile>" > /dev/console
mv $tffile $qffile
else
if [ −f $tffile ]
then
echo −n " <extra: $tffile>" > /dev/console
rm −f $tffile
fi
fi
done
# rename df files with no corresponding qf/hf/Qf files
for dffile in df*
do
qffile=‘echo $dffile | sed ’s/d/q/’‘
hffile=‘echo $dffile | sed ’s/d/h/’‘
Qffile=‘echo $dffile | sed ’s/d/Q/’‘
if [ −r $dffile −a ! −f $qffile −a ! −f $hffile −a ! −f $Qffile ]
then
echo −n " <incomplete: $dffile>" > /dev/console
mv $dffile ‘echo $dffile | sed ’s/d/D/’‘
fi
done
# announce files that have been saved during disaster recovery
for xffile in [A-Z]f*
do
if [ −f $xffile ]
then
echo −n " <panic: $xffile>" > /dev/console
fi
done
SMM:08-14 Sendmail Installation and Operation Guide
Figure 1 — A complex startup script
1.3.16. Map Files
To prevent local denial of service attacks as explained in the top level
README
in the sendmail
distribution, the permissions of map files created by
makemap
should be 0640. The use of 0640 implies
that only trusted users belong to the group assigned to those files. If those files already exist, then it
might be necessary to change the permissions accordingly, e.g.,
cd /etc/mail
chmod 0640 *.db *.pag *.dir
2. NORMAL OPERATIONS
2.1. The System Log
The system log is supported by the
syslogd
(8) program. All messages from
sendmail
are logged un-
der the
LOG_MAIL
facility
5
.
2.1.1. Format
Each line in the system log consists of a timestamp, the name of the machine that generated it (for
logging from several machines over the local area network), the word “sendmail:”, and a message
6
. Most
messages are a sequence of
name
=
value
pairs.
The two most common lines are logged when a message is processed. The first logs the receipt of
a message; there will be exactly one of these per message. Some fields may be omitted if they do not
contain interesting information. Fields are:
from The envelope sender address.
size The size of the message in bytes.
class The class (i.e., numeric precedence) of the message.
pri The initial message priority (used for queue sorting).
nrcpts The number of envelope recipients for this message (after aliasing and forwarding).
msgid The message id of the message (from the header).
bodytype The message body type (7BIT or 8BITMIME), as determined from the envelope.
proto The protocol used to receive this message (e.g., ESMTP or UUCP)
daemon The daemon name from the
DaemonPortOptions
setting.
relay The machine from which it was received.
There is also one line logged per delivery attempt (so there can be several per message if delivery is de-
ferred or there are multiple recipients). Fields are:
to A comma-separated list of the recipients to this mailer.
ctladdr The ‘‘controlling user’’, that is, the name of the user whose credentials we use for de-
livery.
5
Except on Ultrix, which does not support facilities in the syslog.
6
This format may vary slightly if your vendor has changed the syntax.
Sendmail Installation and Operation Guide
SMM:08-15
delay The total delay between the time this message was received and the current delivery at-
tempt.
xdelay The amount of time needed in this delivery attempt (normally indicative of the speed of
the connection).
mailer The name of the mailer used to deliver to this recipient.
relay The name of the host that actually accepted (or rejected) this recipient.
dsn The enhanced error code (RFC 2034) if available.
stat The delivery status.
Not all fields are present in all messages; for example, the relay is usually not listed for local deliveries.
2.1.2. Levels
If you have
syslogd
(8) or an equivalent installed, you will be able to do logging. There is a large
amount of information that can be logged. The log is arranged as a succession of levels. At the lowest
level only extremely strange situations are logged. At the highest level, even the most mundane and un-
interesting events are recorded for posterity. As a convention, log levels under ten are considered gener-
ally “useful;” log levels above 64 are reserved for debugging purposes. Levels from 11−64 are reserved
for verbose information that some sites might want.
A complete description of the log levels is given in section ‘‘Log Level’’.
2.2. Dumping State
You can ask
sendmail
to log a dump of the open files and the connection cache by sending it a
SI-
GUSR1
signal. The results are logged at
LOG_DEBUG
priority.
2.3. The Mail Queues
Mail messages may either be delivered immediately or be held for later delivery. Held messages are
placed into a holding directory called a mail queue.
A mail message may be queued for these reasons:
• If a mail message is temporarily undeliverable, it is queued and delivery is attempted later. If the message
is addressed to multiple recipients, it is queued only for those recipients to whom delivery is not immedi-
ately possible.
• If the SuperSafe option is set to true, all mail messages are queued while delivery is attempted.
• If the DeliveryMode option is set to queue-only or defer, all mail is queued, and no immediate delivery is
attempted.
• If the load average becomes higher than the value of the QueueLA option and the
QueueFactor
(
q
) op-
tion divided by the difference in the current load average and the
QueueLA
option plus one is less than
the priority of the message, messages are queued rather than immediately delivered.
• One or more addresses are marked as expensive and delivery is postponed until the next queue run or one
or more address are marked as held via mailer which uses the hold mailer flag.
• The mail message has been marked as quarantined via a mail filter or rulesets.
2.3.1. Queue Groups and Queue Directories
There are one or more mail queues. Each mail queue belongs to a queue group. There is always a
default queue group that is called ‘‘mqueue’’ (which is where messages go by default unless otherwise
specified). The directory or directories which comprise the default queue group are specified by the
QueueDirectory option. There are zero or more additional named queue groups declared using the
Q
command in the configuration file.
By default, a queued message is placed in the queue group associated with the first recipient in the
recipient list. A recipient address is mapped to a queue group as follows. First, if there is a ruleset called
SMM:08-16 Sendmail Installation and Operation Guide
‘‘queuegroup’’, and if this ruleset maps the address to a queue group name, then that queue group is cho-
sen. That is, the argument for the ruleset is the recipient address (i.e., the address part of the resolved
triple) and the result should be
$#
followed by the name of a queue group. Otherwise, if the mailer asso-
ciated with the address specifies a queue group, then that queue group is chosen. Otherwise, the default
queue group is chosen.
A message with multiple recipients will be split if different queue groups are chosen by the map-
ping of recipients to queue groups.
When a message is placed in a queue group, and the queue group has more than one queue, a
queue is selected randomly.
If a message with multiple recipients is placed into a queue group with the ’r’ option (maximum
number of recipients per message) set to a positive value
N
, and if there are more than
N
recipients in the
message, then the message will be split into multiple messages, each of which have at most
N
recipients.
Notice: if multiple queue groups are used, do
not
move queue files around, e.g., into a different
queue directory. This may have weird effects and can cause mail not to be delivered. Queue files and di-
rectories should be treated as opaque and should not be manipulated directly.
2.3.2. Queue Runs
sendmail
has two different ways to process the queue(s). The first one is to start queue runners af-
ter certain intervals (‘‘normal’’ queue runners), the second one is to keep queue runner processes around
(‘‘persistent’’ queue runners). How to select either of these types is discussed in the appendix ‘‘COM-
MAND LINE FLAGS’’. Persistent queue runners have the advantage that no new processes need to be
spawned at certain intervals; they just sleep for a specified time after they finished a queue run. Another
advantage of persistent queue runners is that only one process belonging to a workgroup (a workgroup is
a set of queue groups) collects the data for a queue run and then multiple queue runner may go ahead us-
ing that data. This can significantly reduce the disk I/O necessary to read the queue files compared to
starting multiple queue runners directly. Their disadvantage is that a new queue run is only started after
all queue runners belonging to a group finished their tasks. In case one of the queue runners tries deliv-
ery to a slow recipient site at the end of a queue run, the next queue run may be substantially delayed. In
general this should be smoothed out due to the distribution of those slow jobs, however, for sites with
small number of queue entries this might introduce noticeable delays. In general, persistent queue run-
ners are only useful for sites with big queues.
2.3.3. Manual Intervention
Under normal conditions the mail queue will be processed transparently. Howev er, you may find
that manual intervention is sometimes necessary. For example, if a major host is down for a period of
time the queue may become clogged. Although
sendmail
ought to recover gracefully when the host
comes up, you may find performance unacceptably bad in the meantime. In that case you want to check
the content of the queue and manipulate it as explained in the next two sections.
2.3.4. Printing the queue
The contents of the queue(s) can be printed using the
mailq
command (or by specifying the
−bp
flag to
sendmail
):
mailq
This will produce a listing of the queue id’s, the size of the message, the date the message entered the
queue, and the sender and recipients. If shared memory support is compiled in, the flag
−bP
can be used
to print the number of entries in the queue(s), provided a process updates the data. However, as ex-
plained earlier, the output might be slightly wrong, since access to the shared memory is not locked. For
example, ‘‘unknown number of entries’’ might be shown. The internal counters are updated after each
queue run to the correct value again.
Sendmail Installation and Operation Guide
SMM:08-17
2.3.5. Forcing the queue
Sendmail
should run the queue automatically at intervals. When using multiple queues, a separate
process will by default be created to run each of the queues unless the queue run is initiated by a user
with the verbose flag. The algorithm is to read and sort the queue, and then to attempt to process all jobs
in order. When it attempts to run the job,
sendmail
first checks to see if the job is locked. If so, it ignores
the job.
There is no attempt to insure that only one queue processor exists at any time, since there is no
guarantee that a job cannot take forever to process (however,
sendmail
does include heuristics to try to
abort jobs that are taking absurd amounts of time; technically, this violates RFC 821, but is blessed by
RFC 1123). Due to the locking algorithm, it is impossible for one job to freeze the entire queue. How-
ev er, an uncooperative recipient host or a program recipient that never returns can accumulate many
processes in your system. Unfortunately, there is no completely general way to solve this.
In some cases, you may find that a major host going down for a couple of days may create a pro-
hibitively large queue. This will result in
sendmail
spending an inordinate amount of time sorting the
queue. This situation can be fixed by moving the queue to a temporary place and creating a new queue.
The old queue can be run later when the offending host returns to service.
To do this, it is acceptable to move the entire queue directory:
cd /var/spool
mv mqueue omqueue; mkdir mqueue; chmod 0700 mqueue
You should then kill the existing daemon (since it will still be processing in the old queue directory) and
create a new daemon.
To run the old mail queue, issue the following command:
/usr/sbin/sendmail −C /etc/mail/queue.cf −q
The
−C
flag specifies an alternate configuration file
queue.cf
which should refer to the moved queue di-
rectory
O QueueDirectory=/var/spool/omqueue
and the
−q
flag says to just run every job in the queue. You can also specify the moved queue directory
on the command line
/usr/sbin/sendmail −oQ/var/spool/omqueue −q
but this requires that you do not have queue groups in the configuration file, because those are not subdi-
rectories of the moved directory. See the section about ‘‘Queue Group Declaration’’ for details; you most
likely need a different configuration file to correctly deal with this problem. However, a proper configu-
ration of queue groups should avoid filling up queue directories, so you shouldn’t run into this problem.
If you have a tendency tow ard voyeurism, you can use the
−v
flag to watch what is going on.
When the queue is finally emptied, you can remove the directory:
rmdir /var/spool/omqueue
2.3.6. Quarantined Queue Items
It is possible to "quarantine" mail messages, otherwise known as envelopes. Envelopes (queue
files) are stored but not considered for delivery or display unless the "quarantine" state of the envelope is
undone or delivery or display of quarantined items is requested. Quarantined messages are tagged by us-
ing a different name for the queue file, ’hf’ instead of ’qf’, and by adding the quarantine reason to the
queue file.
Delivery or display of quarantined items can be requested using the
flag to
sendmail
or
mailq
.
Additionally, messages already in the queue can be quarantined or unquarantined using the new
−Q
flag
to sendmail. For example,
SMM:08-18 Sendmail Installation and Operation Guide
sendmail -Qreason -q[!][I|R|S][matchstring]
Quarantines the normal queue items matching the criteria specified by the
-q[!][I|R|S][matchstring]
us-
ing the reason given on the
−Q
flag. Likewise,
sendmail -qQ -Q[reason] -q[!][I|R|S|Q][matchstring]
Change the quarantine reason for the quarantined items matching the criteria specified by the
-q[!][I|R|S|Q][matchstring]
using the reason given on the
−Q
flag. If there is no reason,
unquarantine the matching items and make them normal queue items. Note that the
flag tells send-
mail to operate on quarantined items instead of normal items.
2.4. Disk Based Connection Information
Sendmail
stores a large amount of information about each remote system it has connected to in mem-
ory. It is possible to preserve some of this information on disk as well, by using the
HostStatusDirectory
op-
tion, so that it may be shared between several invocations of
sendmail
. This allows mail to be queued imme-
diately or skipped during a queue run if there has been a recent failure in connecting to a remote machine.
Note: information about a remote system is stored in a file whose pathname consists of the components of
the hostname in reverse order. For example, the information for
host.example.com
is stored in
com./exam-
ple./host
. For top-level domains like
com
this can create a large number of subdirectories which on some
filesystems can exhaust some limits. Moreover, the performance of lookups in directory with thousands of
entries can be fairly slow depending on the filesystem implementation.
Additionally enabling
SingleThreadDelivery
has the added effect of single-threading mail delivery to
a destination. This can be quite helpful if the remote machine is running an SMTP server that is easily over-
loaded or cannot accept more than a single connection at a time, but can cause some messages to be punted
to a future queue run. It also applies to
all
hosts, so setting this because you have one machine on site that
runs some software that is easily overrun can cause mail to other hosts to be slowed down. If this option is
set, you probably want to set the
MinQueueAge
option as well and run the queue fairly frequently; this way
jobs that are skipped because another
sendmail
is talking to the same host will be tried again quickly rather
than being delayed for a long time.
The disk based host information is stored in a subdirectory of the
mqueue
directory called
.hoststat
7
.
Removing this directory and its subdirectories has an effect similar to the
purgestat
command and is com-
pletely safe. However,
purgestat
only removes expired (Timeout.hoststatus) data. The information in these
directories can be perused with the
hoststat
command, which will indicate the host name, the last access, and
the status of that access. An asterisk in the left most column indicates that a
sendmail
process currently has
the host locked for mail delivery.
The disk based connection information is treated the same way as memory based connection informa-
tion for the purpose of timeouts. By default, information about host failures is valid for 30 minutes. This
can be adjusted with the
Timeout.hoststatus
option.
The connection information stored on disk may be expired at any time with the
purgestat
command or
by invoking sendmail with the
−bH
switch. The connection information may be viewed with the
hoststat
command or by invoking sendmail with the
−bh
switch.
2.5. The Service Switch
The implementation of certain system services such as host and user name lookup is controlled by the
service switch. If the host operating system supports such a switch, and sendmail knows about it,
sendmail
will use the native version. Ultrix, Solaris, and DEC OSF/1 are examples of such systems
8
.
7
This is the usual value of the
HostStatusDirectory
option; it can, of course, go anywhere you like in your filesystem.
8
HP-UX 10 has service switch support, but since the APIs are apparently not available in the libraries
sendmail
does not use the native ser-
vice switch in this release.
Sendmail Installation and Operation Guide
SMM:08-19
If the underlying operating system does not support a service switch (e.g., SunOS 4.X, HP-UX, BSD)
then
sendmail
will provide a stub implementation. The
ServiceSwitchFile
option points to the name of a file
that has the service definitions. Each line has the name of a service and the possible implementations of that
service. For example, the file:
hosts dns files nis
aliases files nis
will ask
sendmail
to look for hosts in the Domain Name System first. If the requested host name is not
found, it tries local files, and if that fails it tries NIS. Similarly, when looking for aliases it will try the local
files first followed by NIS.
Notice: since
sendmail
must access MX records for correct operation, it will use DNS if it is config-
ured in the
ServiceSwitchFile
file. Hence an entry like
hosts files dns
will not avoid DNS lookups even if a host can be found in /etc/hosts.
Note: in contrast to the
sendmail
stub implementation some operating systems do not preserve tempo-
rary failures. For example, if DNS returns a TRY_AGAIN status for this setup
hosts files dns myhostname
but myhostname does not find the requested entry, then a permanent error is returned to
sendmail
which ob-
viously can cause problems, e.g., an immediate bounce instead of a deferral.
Service switches are not completely integrated. For example, despite the fact that the host entry listed
in the above example specifies to look in NIS, on SunOS this won’t happen because the system implementa-
tion of
gethostbyname
(3) doesn’t understand this.
2.6. The Alias Database
After recipient addresses are read from the SMTP connection or command line they are parsed by rule-
set 0, which must resolve to a {
mailer
,
host
,
address
} triple. If the flags selected by the
mailer
include the
A
(aliasable) flag, the
address
part of the triple is looked up as the key (i.e., the left hand side) in the alias
database. If there is a match, the address is deleted from the send queue and all addresses on the right hand
side of the alias are added in place of the alias that was found. This is a recursive operation, so aliases found
in the right hand side of the alias are similarly expanded.
The alias database exists in two forms. One is a text form, maintained in the file
/etc/mail/aliases.
The aliases are of the form
name: name1, name2, ...
Only local names may be aliased; e.g.,
eric@prep.ai.MIT.EDU: eric@CS.Berkeley.EDU
will not have the desired effect (except on prep.ai.MIT.EDU, and they probably don’t want me)
9
. Aliases
may be continued by starting any continuation lines with a space or a tab or by putting a backslash directly
before the newline. Blank lines and lines beginning with a sharp sign (“#”) are comments.
The second form is processed by one of the available map types, e.g.,
ndbm
(3)
10
the Berkeley DB li-
brary, or
cdb
. This is the form that
sendmail
actually uses to resolve aliases. This technique is used to im-
prove performance.
The control of search order is actually set by the service switch. Essentially, the entry
9
Actually, any mailer that has the ‘A’ mailer flag set will permit aliasing; this is normally limited to the local mailer.
10
The
gdbm
package does not work.
SMM:08-20 Sendmail Installation and Operation Guide
O AliasFile=switch:aliases
is always added as the first alias entry; also, the first alias file name without a class (e.g., without “nis:” on
the front) will be used as the name of the file for a ‘‘files’’ entry in the aliases switch. For example, if the
configuration file contains
O AliasFile=/etc/mail/aliases
and the service switch contains
aliases nis files nisplus
then aliases will first be searched in the NIS database, then in /etc/mail/aliases, then in the NIS+ database.
You can also use
NIS
-based alias files. For example, the specification:
O AliasFile=/etc/mail/aliases
O AliasFile=nis:mail.aliases@my.nis.domain
will first search the /etc/mail/aliases file and then the map named “mail.aliases” in “my.nis.domain”. Warn-
ing: if you build your own
NIS
-based alias files, be sure to provide the
−l
flag to
makedbm
(8) to map upper
case letters in the keys to lower case; otherwise, aliases with upper case letters in their names won’t match
incoming addresses.
Additional flags can be added after the colon exactly like a
K
line — for example:
O AliasFile=nis:−N mail.aliases@my.nis.domain
will search the appropriate NIS map and always include null bytes in the key. Also:
O AliasFile=nis:−f mail.aliases@my.nis.domain
will prevent sendmail from downcasing the key before the alias lookup.
2.6.1. Rebuilding the alias database
The
hash
or
dbm
version of the database may be rebuilt explicitly by executing the command
newaliases
This is equivalent to giving
sendmail
the
−bi
flag:
/usr/sbin/sendmail −bi
If you have multiple aliases databases specified, the
−bi
flag rebuilds all the database types it un-
derstands (for example, it can rebuild NDBM databases but not NIS databases).
2.6.2. Potential problems
There are a number of problems that can occur with the alias database. They all result from a
sendmail
process accessing the DBM version while it is only partially built. This can happen under two
circumstances: One process accesses the database while another process is rebuilding it, or the process
rebuilding the database dies (due to being killed or a system crash) before completing the rebuild.
Sendmail has three techniques to try to relieve these problems. First, it ignores interrupts while re-
building the database; this avoids the problem of someone aborting the process leaving a partially rebuilt
database. Second, it locks the database source file during the rebuild — but that may not work over NFS
or if the file is unwritable. Third, at the end of the rebuild it adds an alias of the form
@: @
(which is not normally legal). Before
sendmail
will access the database, it checks to insure that this entry
Sendmail Installation and Operation Guide
SMM:08-21
exists
11
.
2.6.3. List owners
If an error occurs on sending to a certain address, say “
x
”,
sendmail
will look for an alias of the
form “owner-
x
” to receive the errors. This is typically useful for a mailing list where the submitter of the
list has no control over the maintenance of the list itself; in this case the list maintainer would be the
owner of the list. For example:
unix-wizards: eric@ucbarpa, wnj@monet, nosuchuser,
sam@matisse
owner-unix-wizards: unix-wizards-request
unix-wizards-request: eric@ucbarpa
would cause “eric@ucbarpa” to get the error that will occur when someone sends to unix-wizards due to
the inclusion of “nosuchuser” on the list.
List owners also cause the envelope sender address to be modified. The contents of the owner alias
are used if they point to a single user, otherwise the name of the alias itself is used. For this reason, and
to obey Internet conventions, the “owner-” address normally points at the “-request” address; this causes
messages to go out with the typical Internet convention of using ‘‘
list
-request’’ as the return address.
2.7. User Information Database
This option is deprecated, use virtusertable and genericstable instead as explained in
cf/README
. If
you have a version of
sendmail
with the user information database compiled in, and you have specified one
or more databases using the
U
option, the databases will be searched for a
user
:maildrop entry. If found, the
mail will be sent to the specified address.
2.8. Per-User Forwarding (.forward Files)
As an alternative to the alias database, any user may put a file with the name “.forward” in his or her
home directory. If this file exists,
sendmail
redirects mail for that user to the list of addresses listed in the
.forward file. Note that aliases are fully expanded before forward files are referenced. For example, if the
home directory for user “mckusick” has a .forward file with contents:
mckusick@ernie
kirk@calder
then any mail arriving for “mckusick” will be redirected to the specified accounts.
Actually, the configuration file defines a sequence of filenames to check. By default, this is the user’s
.forward file, but can be defined to be more generally using the
ForwardPath
option. If you change this,
you will have to inform your user base of the change; .forward is pretty well incorporated into the collective
subconscious.
2.9. Special Header Lines
Several header lines have special interpretations defined by the configuration file. Others have inter-
pretations built into
sendmail
that cannot be changed without changing the code. These built-ins are de-
scribed here.
2.9.1. Errors-To:
If errors occur anywhere during processing, this header will cause error messages to go to the listed
addresses. This is intended for mailing lists.
11
The
AliasWait
option is required in the configuration for this action to occur. This should normally be specified.
SMM:08-22 Sendmail Installation and Operation Guide
The Errors-To: header was created in the bad old days when UUCP didn’t understand the distinc-
tion between an envelope and a header; this was a hack to provide what should now be passed as the en-
velope sender address. It should go away. It is only used if the
UseErrorsTo
option is set.
The Errors-To: header is officially deprecated and will go away in a future release.
2.9.2. Apparently-To:
RFC 822 requires at least one recipient field (To:, Cc:, or Bcc: line) in every message. If a message
comes in with no recipients listed in the message then
sendmail
will adjust the header based on the
“NoRecipientAction” option. One of the possible actions is to add an “Apparently-To:” header line for
any recipients it is aware of.
The Apparently-To: header is non-standard and is both deprecated and strongly discouraged.
2.9.3. Precedence
The Precedence: header can be used as a crude control of message priority. It tweaks the sort order
in the queue and can be configured to change the message timeout values. The precedence of a message
also controls how delivery status notifications (DSNs) are processed for that message.
2.10. IDENT Protocol Support
Sendmail
supports the IDENT protocol as defined in RFC 1413. Note that the RFC states a client
should wait at least 30 seconds for a response. The default Timeout.ident is 5 seconds as many sites have
adopted the practice of dropping IDENT queries. This has lead to delays processing mail. Although this en-
hances identification of the author of an email message by doing a ‘‘call back’’ to the originating system to
include the owner of a particular TCP connection in the audit trail it is in no sense perfect; a determined
forger can easily spoof the IDENT protocol. The following description is excerpted from RFC 1413:
6. Security Considerations
The information returned by this protocol is at most as trustworthy as the host providing it OR the or-
ganization operating the host. For example, a PC in an open lab has few if any controls on it to prevent
a user from having this protocol return any identifier the user wants. Likewise, if the host has been
compromised the information returned may be completely erroneous and misleading.
The Identification Protocol is not intended as an authorization or access control protocol. At best, it
provides some additional auditing information with respect to TCP connections. At worst, it can pro-
vide misleading, incorrect, or maliciously incorrect information.
The use of the information returned by this protocol for other than auditing is strongly discouraged.
Specifically, using Identification Protocol information to make access control decisions - either as the
primary method (i.e., no other checks) or as an adjunct to other methods may result in a weakening of
normal host security.
An Identification server may reveal information about users, entities, objects or processes which might
normally be considered private. An Identification server provides service which is a rough analog of
the CallerID services provided by some phone companies and many of the same privacy considerations
and arguments that apply to the CallerID service apply to Identification. If you wouldn’t run a "finger"
server due to privacy considerations you may not want to run this protocol.
In some cases your system may not work properly with IDENT support due to a bug in the TCP/IP imple-
mentation. The symptoms will be that for some hosts the SMTP connection will be closed almost immedi-
ately. If this is true or if you do not want to use IDENT, you should set the IDENT timeout to zero; this will
disable the IDENT protocol.
3. ARGUMENTS
The complete list of arguments to
sendmail
is described in detail in Appendix A. Some important argu-
ments are described here.
Sendmail Installation and Operation Guide
SMM:08-23
3.1. Queue Interval
The amount of time between forking a process to run through the queue is defined by the
−q
flag. If
you run with delivery mode set to
i
or
b
this can be relatively large, since it will only be relevant when a host
that was down comes back up. If you run in
q
mode it should be relatively short, since it defines the maxi-
mum amount of time that a message may sit in the queue. (See also the MinQueueAge option.)
RFC 1123 section 5.3.1.1 says that this value should be at least 30 minutes (although that probably
doesn’t make sense if you use ‘‘queue-only’’ mode).
Notice: the meaning of the interval time depends on whether normal queue runners or persistent queue
runners are used. For the former, it is the time between subsequent starts of a queue run. For the latter, it is
the time sendmail waits after a persistent queue runner has finished its work to start the next one. Hence for
persistent queue runners this interval should be very low, typically no more than two minutes.
3.2. Daemon Mode
If you allow incoming mail over an IPC connection, you should have a daemon running. This should
be set by your
/etc/rc
file using the
−bd
flag. The
−bd
flag and the
−q
flag may be combined in one call:
/usr/sbin/sendmail −bd −q30m
An alternative approach is to invoke sendmail from
inetd
(8) (use the
−bs
−Am flags to ask sendmail to
speak SMTP on its standard input and output and to run as MTA). This works and allows you to wrap
send-
in a TCP wrapper program, but may be a bit slower since the configuration file has to be re-read on
ev ery message that comes in. If you do this, you still need to have a
sendmail
running to flush the queue:
/usr/sbin/sendmail −q30m
3.3. Forcing the Queue
In some cases you may find that the queue has gotten clogged for some reason. You can force a queue
run using the
−q
flag (with no value). It is entertaining to use the
−v
flag (verbose) when this is done to
watch what happens:
/usr/sbin/sendmail −q −v
You can also limit the jobs to those with a particular queue identifier, recipient, sender, quarantine rea-
son, or queue group using one of the queue modifiers. For example, “−qRberkeley” restricts the queue run to
jobs that have the string “berkeley” somewhere in one of the recipient addresses. Similarly, “−qSstring” lim-
its the run to particular senders, “−qIstring” limits it to particular queue identifiers, and “−qQstring” limits it
to particular quarantined reasons and only operated on quarantined queue items, and “−qGstring” limits it to
a particular queue group. The named queue group will be run even if it is set to have 0 runners. You may
also place an
!
before the
I
or
R
or
S
or
Q
to indicate that jobs are limited to not including a particular queue
identifier, recipient or sender. For example, “−q!Rseattle” limits the queue run to jobs that do not have the
string “seattle” somewhere in one of the recipient addresses. Should you need to terminate the queue jobs
currently active then a SIGTERM to the parent of the process (or processes) will cleanly stop the jobs.
3.4. Debugging
There are a fairly large number of debug flags built into
sendmail
. Each debug flag has a category and
a lev el. Higher levels increase the level of debugging activity; in most cases, this means to print out more in-
formation. The convention is that levels greater than nine are “absurd,” i.e., they print out so much informa-
tion that you wouldn’t normally want to see them except for debugging that particular piece of code.
You should
never
run a production sendmail server in debug mode. Many of the debug flags will re-
sult in debug output being sent over the SMTP channel unless the option
−D
is used. This will confuse many
mail programs. However, for testing purposes, it can be useful when sending mail manually via telnet to the
port you are using while debugging.
SMM:08-24 Sendmail Installation and Operation Guide
A debug category is either an integer, like 42, or a name, like ANSI. You can specify a range of nu-
meric debug categories using the syntax 17-42. You can specify a set of named debug categories using a
glob pattern like “sm_trace_*”. At present, only “*” and “?” are supported in these glob patterns.
Debug flags are set using the
−d
option; the syntax is:
debug-flag:
−d
debug-list
debug-list: debug-option [ , debug-option ]*
debug-option: debug-categories [ . debug-level ]
debug-categories: integer | integer − integer | category-pattern
category-pattern: [a-zA-Z_*?][a-zA-Z0-9_*?]*
debug-level: integer
where spaces are for reading ease only. For example,
−d12 Set category 12 to level 1
−d12.3 Set category 12 to level 3
−d3−17 Set categories 3 through 17 to level 1
−d3−17.4 Set categories 3 through 17 to level 4
−dANSI Set category ANSI to level 1
−dsm_trace_*.3 Set all named categories matching sm_trace_* to level 3
For a complete list of the available debug flags you will have to look at the code and the
TRACEFLAGS
file
in the sendmail distribution (they are too dynamic to keep this document up to date). For a list of named de-
bug categories in the sendmail binary, use
ident /usr/sbin/sendmail | grep Debug
3.5. Changing the Values of Options
Options can be overridden using the
−o
or
−O
command line flags. For example,
/usr/sbin/sendmail −oT2m
sets the
T
(timeout) option to two minutes for this run only; the equivalent line using the long option name is
/usr/sbin/sendmail -OTimeout.queuereturn=2m
Some options have security implications. Sendmail allows you to set these, but relinquishes its set-
user-ID or set-group-ID permissions thereafter
12
.
3.6. Trying a Different Configuration File
An alternative configuration file can be specified using the
−C
flag; for example,
/usr/sbin/sendmail −Ctest.cf −oQ/tmp/mqueue
uses the configuration file
test.cf
instead of the default
/etc/mail/sendmail.cf.
If the
−C
flag has no value it
defaults to
sendmail.cf
in the current directory.
Sendmail
gives up set-user-ID root permissions (if it has been installed set-user-ID root) when you use
this flag, so it is common to use a publicly writable directory (such as /tmp) as the queue directory (QueueDi-
rectory or Q option) while testing.
3.7. Logging Traffic
Many SMTP implementations do not fully implement the protocol. For example, some personal com-
puter based SMTPs do not understand continuation lines in reply codes. These can be very hard to trace. If
12
That is, it sets its effective uid to the real uid; thus, if you are executing as root, as from root’s crontab file or during system startup the
root permissions will still be honored.
Sendmail Installation and Operation Guide
SMM:08-25
you suspect such a problem, you can set traffic logging using the
−X
flag. For example,
/usr/sbin/sendmail −X /tmp/traffic −bd
will log all traffic in the file
/tmp/traffic
.
This logs a lot of data very quickly and should
NEVER
be used during normal operations. After start-
ing up such a daemon, force the errant implementation to send a message to your host. All message traffic in
and out of
sendmail
, including the incoming SMTP traffic, will be logged in this file.
3.8. Testing Configuration Files
When you build a configuration table, you can do a certain amount of testing using the “test mode” of
sendmail
. For example, you could invoke
sendmail
as:
sendmail −bt −Ctest.cf
which would read the configuration file “test.cf” and enter test mode. In this mode, you enter lines of the
form:
rwset address
where
rwset
is the rewriting set you want to use and
address
is an address to apply the set to. Test mode
shows you the steps it takes as it proceeds, finally showing you the address it ends up with. You may use a
comma separated list of rwsets for sequential application of rules to an input. For example:
3,1,21,4 monet:bollard
first applies ruleset three to the input “monet:bollard.” Ruleset one is then applied to the output of ruleset
three, followed similarly by rulesets twenty-one and four.
If you need more detail, you can also use the “−d21” flag to turn on more debugging. For example,
sendmail −bt −d21.99
turns on an incredible amount of information; a single word address is probably going to print out several
pages worth of information.
You should be warned that internally,
sendmail
applies ruleset 3 to all addresses. In test mode you will
have to do that manually. For example, older versions allowed you to use
0 bruce@broadcast.sony.com
This version requires that you use:
3,0 bruce@broadcast.sony.com
As of version 8.7, some other syntaxes are available in test mode:
.D x value defines macro
x
to have the indicated
value
. This is useful when debugging rules that use
the
$&
x
syntax.
.C c value adds the indicated
value
to class
c
.
=S ruleset
dumps the contents of the indicated ruleset.
−d debug-spec is equivalent to the command-line flag.
Version 8.9 introduced more features:
?
shows a help message.
=M display the known mailers.
$m print the value of macro m.
$=c print the contents of class c.
/mx host
returns the MX records for ‘host’.
SMM:08-26 Sendmail Installation and Operation Guide
/parse address
parse address, returning the value of
crackaddr
, and the parsed address.
/try mailer addr rewrite address into the form it will have when presented to the indicated mailer.
/tryflags flags
set flags used by parsing. The flags can be ‘H’ for Header or ‘E’ for Envelope, and ‘S’ for
Sender or ‘R’ for Recipient. These can be combined, ‘HR’ sets flags for header recipients.
/canon hostname try to canonify hostname.
/map mapname key
look up ‘key’ in the indicated ‘mapname’.
/quit quit address test mode.
3.9. Persistent Host Status Information
When
HostStatusDirectory
is enabled, information about the status of hosts is maintained on disk and
can thus be shared between different instantiations of
sendmail
. The status of the last connection with each
remote host may be viewed with the command:
sendmail −bh
This information may be flushed with the command:
sendmail −bH
Flushing the information prevents new
sendmail
processes from loading it, but does not prevent existing
processes from using the status information that they already have.
4. TUNING
There are a number of configuration parameters you may want to change, depending on the requirements
of your site. Most of these are set using an option in the configuration file. For example, the line “O Time-
out.queuereturn=5d” sets option “Timeout.queuereturn” to the value “5d” (five days).
Most of these options have appropriate defaults for most sites. However, sites having very high mail loads
may find they need to tune them as appropriate for their mail load. In particular, sites experiencing a large num-
ber of small messages, many of which are delivered to many recipients, may find that they need to adjust the pa-
rameters dealing with queue priorities.
All versions of
sendmail
prior to 8.7 had single character option names. As of 8.7, options have long
(multi-character names). Although old short names are still accepted, most new options do not have short equiv-
alents.
This section only describes the options you are most likely to want to tweak; read section 5 for more de-
tails.
4.1. Timeouts
All time intervals are set using a scaled syntax. For example, “10m” represents ten minutes, whereas
“2h30m” represents two and a half hours. The full set of scales is:
s
seconds
m
minutes
h
hours
d
days
w
weeks
4.1.1. Queue interval
The argument to the
−q
flag specifies how often a sub-daemon will run the queue. This is typically
set to between fifteen minutes and one hour. If not set, or set to zero, the queue will not be run automati-
cally. RFC 1123 section 5.3.1.1 recommends that this be at least 30 minutes. Should you need to termi-
nate the queue jobs currently active then a SIGTERM to the parent of the process (or processes) will
Sendmail Installation and Operation Guide
SMM:08-27
cleanly stop the jobs.
4.1.2. Read timeouts
Timeouts all have option names “Timeout.
suboption
”. Most of these control SMTP operations.
The recognized
suboption
s, their default values, and the minimum values allowed by RFC 2821 section
4.5.3.2 (or RFC 1123 section 5.3.2) are:
connect The time to wait for an SMTP connection to open (the
connect
(2) system call) [0, un-
specified]. If zero, uses the kernel default. In no case can this option extend the time-
out longer than the kernel provides, but it can shorten it. This is to get around kernels
that provide an absurdly long connection timeout (90 minutes in one case).
iconnect The same as
connect,
except it applies only to the initial attempt to connect to a host
for a given message [0, unspecified]. The concept is that this should be very short (a
few seconds); hosts that are well connected and responsive will thus be serviced imme-
diately. Hosts that are slow will not hold up other deliveries in the initial delivery at-
tempt.
aconnect [0, unspecified] The overall timeout waiting for all connection for a single delivery at-
tempt to succeed. If 0, no overall limit is applied. This can be used to restrict the total
amount of time trying to connect to a long list of host that could accept an e-mail for
the recipient. This timeout does not apply to
FallbackMXhost
, i.e., if the time is ex-
hausted, the
FallbackMXhost
is tried next.
initial The wait for the initial 220 greeting message [5m, 5m].
helo The wait for a reply from a HELO or EHLO command [5m, unspecified]. This may re-
quire a host name lookup, so five minutes is probably a reasonable minimum.
mail† The wait for a reply from a MAIL command [10m, 5m].
rcpt† The wait for a reply from a RCPT command [1h, 5m]. This should be long because it
could be pointing at a list that takes a long time to expand (see below).
datainit† The wait for a reply from a DAT A command [5m, 2m].
datablock†‡ The wait for reading a data block (that is, the body of the message). [1h, 3m]. This
should be long because it also applies to programs piping input to
sendmail
which have
no guarantee of promptness.
datafinal† The wait for a reply from the dot terminating a message. [1h, 10m]. If this is shorter
than the time actually needed for the receiver to deliver the message, duplicates will be
generated. This is discussed in RFC 1047.
rset The wait for a reply from a RSET command [5m, unspecified].
quit The wait for a reply from a QUIT command [2m, unspecified].
misc The wait for a reply from miscellaneous (but short) commands such as NOOP (no-op-
eration) and VERB (go into verbose mode). [2m, unspecified].
command†‡ In server SMTP, the time to wait for another command. [1h, 5m].
ident‡ The timeout waiting for a reply to an IDENT query [5s
13
, unspecified].
lhlo The wait for a reply to an LMTP LHLO command [2m, unspecified].
auth The timeout for a reply in an SMTP AUTH dialogue [10m, unspecified].
13
On some systems the default is zero to turn the protocol off entirely.
SMM:08-28 Sendmail Installation and Operation Guide
starttls The timeout for a reply to an SMTP STARTTLS command and the TLS handshake [1h,
unspecified].
fileopen‡ The timeout for opening .forward and :include: files [60s, none].
control‡ The timeout for a complete control socket transaction to complete [2m, none].
hoststatus‡ How long status information about a host (e.g., host down) will be cached before it is
considered stale [30m, unspecified].
resolver.retrans‡ The resolver’s retransmission time interval (in seconds) [varies]. Sets both
Timeout.re-
solver.retrans.first
and
Timeout.resolver.retrans.normal
.
resolver.retrans.first‡
The resolver’s retransmission time interval (in seconds) for the first attempt to deliver a
message [varies].
resolver.retrans.normal‡
The resolver’s retransmission time interval (in seconds) for all resolver lookups except
the first delivery attempt [varies].
resolver.retry‡ The number of times to retransmit a resolver query.
Sets both
Timeout.re-
solver.retry.first
and
Timeout.resolver.retry.normal
[varies].
resolver.retry.first‡
The number of times to retransmit a resolver query for the first attempt to deliver a
message [varies].
resolver.retry.normal‡
The number of times to retransmit a resolver query for all resolver lookups
except the first delivery attempt [varies].
For compatibility with old configuration files, if no
suboption
is specified, all the timeouts marked with a
dagger (†) are set to the indicated value. All but those marked with a double dagger (‡) apply to client
SMTP.
For example, the lines:
O Timeout.command=25m
O Timeout.datablock=3h
sets the server SMTP command timeout to 25 minutes and the input data block timeout to three hours.
4.1.3. Message timeouts
After sitting in the queue for a few days, an undeliverable message will time out. This is to insure
that at least the sender is aware of the inability to send a message. The timeout is typically set to five
days. It is sometimes considered convenient to also send a warning message if the message is in the
queue longer than a few hours (assuming you normally have good connectivity; if your messages nor-
mally took several hours to send you wouldn’t want to do this because it wouldn’t be an unusual event).
These timeouts are set using the
Timeout.queuereturn
and
Timeout.queuewarn
options in the configu-
ration file (previously both were set using the
T
option).
If the message is submitted using the
NOTIFY SMTP
extension, warning messages will only be sent
if
NOTIFY=DELAY
is specified. The queuereturn and queuewarn timeouts can be further qualified with a
tag based on the Precedence: field in the message; they must be one of “urgent” (indicating a positive
non-zero precedence), “normal” (indicating a zero precedence), or “non-urgent” (indicating negative
precedences). For example, setting “Timeout.queuewarn.urgent=1h” sets the warning timeout for urgent
messages only to one hour. The default if no precedence is indicated is to set the timeout for all prece-
dences. If the message has a normal (default) precedence and it is a delivery status notification (DSN),
Timeout.queuereturn.dsn
and
Timeout.queuewarn.dsn
can be used to give an alternative warn and re-
turn time for DSNs. The value "now" can be used for -O Timeout.queuereturn to return entries immedi-
ately during a queue run, e.g., to bounce messages independent of their time in the queue.
Sendmail Installation and Operation Guide
SMM:08-29
Since these options are global, and since you cannot know
a priori
how long another host outside
your domain will be down, a five day timeout is recommended. This allows a recipient to fix the problem
ev en if it occurs at the beginning of a long weekend. RFC 1123 section 5.3.1.1 says that this parameter
should be ‘‘at least 4−5 days’’.
The
Timeout.queuewarn
value can be piggybacked on the
T
option by indicating a time after
which a warning message should be sent; the two timeouts are separated by a slash. For example, the
line
OT5d/4h
causes email to fail after five days, but a warning message will be sent after four hours. This should be
large enough that the message will have been tried several times.
4.2. Forking During Queue Runs
By setting the
ForkEachJob
(
Y
) option,
sendmail
will fork before each individual message while run-
ning the queue. This option was used with earlier releases to prevent
sendmail
from consuming large
amounts of memory. It should no longer be necessary with
sendmail
8.12. If the
ForkEachJob
option is
not set,
sendmail
will keep track of hosts that are down during a queue run, which can improve performance
dramatically.
If the
ForkEachJob
option is set,
sendmail
cannot use connection caching.
4.3. Queue Priorities
Every message is assigned a priority when it is first instantiated, consisting of the message size (in
bytes) offset by the message class (which is determined from the Precedence: header) times the “work class
factor” and the number of recipients times the “work recipient factor.” The priority is used to order the
queue. Higher numbers for the priority mean that the message will be processed later when running the
queue.
The message size is included so that large messages are penalized relative to small messages. The
message class allows users to send “high priority” messages by including a “Precedence:” field in their mes-
sage; the value of this field is looked up in the
P
lines of the configuration file. Since the number of recipi-
ents affects the amount of load a message presents to the system, this is also included into the priority.
The recipient and class factors can be set in the configuration file using the
RecipientFactor
(
y
) and
ClassFactor
(
z
) options respectively. They default to 30000 (for the recipient factor) and 1800 (for the class
factor). The initial priority is:
pri
=
msgsize
−
(
class
×
ClassFactor)
+
(
nrcpt
×
RecipientFactor)
(Remember, higher values for this parameter actually mean that the job will be treated with lower priority.)
The priority of a job can also be adjusted each time it is processed (that is, each time an attempt is
made to deliver it) using the “work time factor,” set by the
RetryFactor
(
Z
) option. This is added to the pri-
ority, so it normally decreases the precedence of the job, on the grounds that jobs that have failed many times
will tend to fail again in the future. The
RetryFactor
option defaults to 90000.
4.4. Load Limiting
Sendmail
can be asked to queue (but not deliver) mail if the system load average gets too high using
the
QueueLA
(
x
) option. When the load average exceeds the value of the
QueueLA
option, the delivery
mode is set to
q
(queue only) if the
QueueFactor
(
q
) option divided by the difference in the current load av-
erage and the
QueueLA
option plus one is less than the priority of the message — that is, the message is
queued iff:
pri
>
QueueFactor
LA
−
QueueLA
+
1
The
QueueFactor
option defaults to 600000, so each point of load average is worth 600000 priority points
SMM:08-30 Sendmail Installation and Operation Guide
(as described above).
For drastic cases, the
RefuseLA
(
X
) option defines a load average at which
sendmail
will refuse to ac-
cept network connections. Locally generated mail, i.e., mail which is not submitted via SMTP (including in-
coming UUCP mail), is still accepted. Notice that the MSP submits mail to the MTA via SMTP, and hence
mail will be queued in the client queue in such a case. Therefore it is necessary to run the client mail queue
periodically.
4.5. Resource Limits
Sendmail
has several parameters to control resource usage. Besides those mentioned in the previous
section, there are at least
MaxDaemonChildren
,
ConnectionRateThrottle
,
MaxQueueChildren
, and
MaxRunnersPerQueue
. The latter two limit the number of
sendmail
processes that operate on the queue.
These are discussed in the section ‘‘Queue Group Declaration’’. The former two can be used to limit the
number of incoming connections. Their appropriate values depend on the host operating system and the
hardware, e.g., amount of memory. In many situations it might be useful to set limits to prevent to have too
many
sendmail
processes, however, these limits can be abused to mount a denial of service attack. For ex-
ample, if
MaxDaemonChildren=10
then an attacker needs to open only 10 SMTP sessions to the server,
leave them idle for most of the time, and no more connections will be accepted. If this option is set then the
timeouts used in a SMTP session should be lowered from their default values to their minimum values as
specified in RFC 2821 and listed in section 4.1.2.
4.6. Measures against Denial of Service Attacks
Sendmail
has some built-in measures against simple denial of service (DoS) attacks. The SMTP
server by default slows down if too many bad commands are issued or if some commands are repeated too
often within a session. Details can be found in the source file
sendmail/srvrsmtp.c
by looking for the macro
definitions of
MAXBADCOMMANDS
,
MAXNOOPCOMMANDS
,
MAXHELOCOMMANDS
,
MAXVRFYCOMMANDS
, and
MAXETRNCOMMANDS
. If an SMTP command is issued more often
than the corresponding
MAXcmdCOMMANDS
value, then the response is delayed exponentially, starting
with a sleep time of one second, up to a maximum of four minutes (as defined by
MAXTIMEOUT
). If the
option
MaxDaemonChildren
is set to a value greater than zero, then this could make a DoS attack even
worse since it keeps a connection open longer than necessary. Therefore a connection is terminated with a
421 SMTP reply code if the number of commands exceeds the limit by a factor of two and
MAXBADCOM-
MANDS
is set to a value greater than zero (the default is 25).
4.7. Delivery Mode
There are a number of delivery modes that
sendmail
can operate in, set by the
DeliveryMode
(
d
) con-
figuration option. These modes specify how quickly mail will be delivered. Legal modes are:
i
deliver interactively (synchronously)
b
deliver in background (asynchronously)
q
queue only (don’t deliver)
d
defer delivery attempts (don’t deliver)
There are tradeoffs. Mode “i” gives the sender the quickest feedback, but may slow down some mailers and
is hardly ever necessary. Mode “b” delivers promptly but can cause large numbers of processes if you have a
mailer that takes a long time to deliver a message. Mode “q” minimizes the load on your machine, but
means that delivery may be delayed for up to the queue interval. Mode “d” is identical to mode “q” except
that it also prevents lookups in maps including the
-D
flag from working during the initial queue phase; it is
intended for ‘‘dial on demand’’ sites where DNS lookups might cost real money. Some simple error mes-
sages (e.g., host unknown during the SMTP protocol) will be delayed using this mode. Mode “b” is the
usual default.
If you run in mode “q” (queue only), “d” (defer), or “b” (deliver in background)
sendmail
will not ex-
pand aliases and follow .forward files upon initial receipt of the mail. This speeds up the response to RCPT
commands. Mode “i” should not be used by the SMTP server.
Sendmail Installation and Operation Guide
SMM:08-31
4.8. Log Level
The level of logging can be set for
sendmail
. The default using a standard configuration is level 9.
The levels are approximately as follows (some log types are using different level depending on various fac-
tors):
0
Minimal logging.
1
Serious system failures and potential security problems.
2
Lost communications (network problems) and protocol failures.
3
Other serious failures, malformed addresses, transient forward/include errors, connection timeouts.
4
Minor failures, out of date alias databases, connection rejections via check_ rulesets.
5
Message collection statistics.
6
Creation of error messages, VRFY and EXPN commands.
7
Delivery failures (host or user unknown, etc.).
8
Successful deliveries and alias database rebuilds.
9
Messages being deferred (due to a host being down, etc.).
10 Database expansion (alias, forward, and userdb lookups) and authentication information.
11 NIS errors and end of job processing.
12 Logs all SMTP connections.
13 Log bad user shells, files with improper permissions, and other questionable situations.
14 Logs refused connections.
15 Log all incoming SMTP commands.
20 Logs attempts to run locked queue files. These are not errors, but can be useful to note if your
queue appears to be clogged.
30 Lost locks (only if using lockf instead of flock).
Additionally, values above 64 are reserved for extremely verbose debugging output. No normal site would
ev er set these.
4.9. File Modes
The modes used for files depend on what functionality you want and the level of security you require.
In many cases
sendmail
does careful checking of the modes of files and directories to avoid accidental com-
promise; if you want to make it possible to have group-writable support files you may need to use the
Dont-
BlameSendmail
option to turn off some of these checks.
4.9.1. To suid or not to suid?
Sendmail
is no longer installed set-user-ID to root. sendmail/SECURITY explains how to config-
ure and install
sendmail
without set-user-ID to root but set-group-ID which is the default configuration
starting with 8.12.
The daemon usually runs as root, unless other measures are taken. At the point where
sendmail
is
about to
exec
(2) a mailer, it checks to see if the userid is zero (root); if so, it resets the userid and groupid
to a default (set by the
U=
equate in the mailer line; if that is not set, the
DefaultUser
option is used).
This can be overridden by setting the
S
flag to the mailer for mailers that are trusted and must be called as
root. However, this will cause mail processing to be accounted (using
sa
(8)) to root rather than to the
user sending the mail.
A middle ground is to set the
RunAsUser
option. This causes
sendmail
to become the indicated
user as soon as it has done the startup that requires root privileges (primarily, opening the
SMTP
socket).
If you use
RunAsUser
, the queue directory (normally
/var/spool/mqueue
) should be owned by that user,
SMM:08-32 Sendmail Installation and Operation Guide
and all files and databases (including user
.forward
files, alias files, :include: files, and external data-
bases) must be readable by that user. Also, since sendmail will not be able to change its uid, delivery to
programs or files will be marked as unsafe, e.g., undeliverable, in
.forward
, aliases, and :include: files.
Administrators can override this by setting the
DontBlameSendmail
option to the setting
NonRoot-
SafeAddr
.
RunAsUser
is probably best suited for firewall configurations that don’t hav e regular user lo-
gins. If the option is used on a system which performs local delivery, then the local delivery agent must
have the proper permissions (i.e., usually set-user-ID root) since it will be invoked by the
RunAsUser
,
not by root.
4.9.2. Turning off security checks
Sendmail
is very particular about the modes of files that it reads or writes. For example, by default
it will refuse to read most files that are group writable on the grounds that they might have been tampered
with by someone other than the owner; it will even refuse to read files in group writable directories.
Also, sendmail will refuse to create a new aliases database in an unsafe directory. You can get around
this by manually creating the database file as a trusted user ahead of time and then rebuilding the aliases
database with
newaliases
.
If you are
quite
sure that your configuration is safe and you want
sendmail
to avoid these security
checks, you can turn off certain checks using the
DontBlameSendmail
option. This option takes one or
more names that disable checks. In the descriptions that follow, “unsafe directory” means a directory that
is writable by anyone other than the owner. The values are:
Safe No special handling.
AssumeSafeChown
Assume that the
chown
system call is restricted to root. Since some versions of UNIX permit
regular users to give away their files to other users on some filesystems,
sendmail
often cannot
assume that a given file was created by the owner, particularly when it is in a writable directory.
You can set this flag if you know that file giveaw ay is restricted on your system.
CertOwner
Accept certificate public and private key files which are not owned by RunAsUser for START-
TLS.
ClassFileInUnsafeDirPath
When reading class files (using the
F
line in the configuration file), allow files that are in unsafe
directories.
DontWarnForwardFileInUnsafeDirPath
Prevent logging of unsafe directory path warnings for non-existent forward files.
ErrorHeaderInUnsafeDirPath
Allow the file named in the
ErrorHeader
option to be in an unsafe directory.
FileDeliveryToHardLink
Allow delivery to files that are hard links.
FileDeliveryToSymLink
Allow delivery to files that are symbolic links.
ForwardFileInGroupWritableDirPath
Allow
.forward
files in group writable directories.
ForwardFileInUnsafeDirPath
Allow
.forward
files in unsafe directories.
ForwardFileInUnsafeDirPathSafe
Allow a
.forward
file that is in an unsafe directory to include references to program and files.
GroupReadableKeyFile
Accept a group-readable key file for STARTTLS.
Sendmail Installation and Operation Guide
SMM:08-33
GroupReadableSASLDBFile
Accept a group-readable Cyrus SASL password file.
GroupReadableDefaultAuthInfoFile
Accept a group-readable DefaultAuthInfo file for SASL.
GroupWritableAliasFile
Allow group-writable alias files.
GroupWritableDirPathSafe
Change the definition of “unsafe directory” to consider group-writable directories to be safe.
World-writable directories are always unsafe.
GroupWritableForwardFile
Allow group writable
.forward
files.
GroupWritableForwardFileSafe
Accept group-writable
.forward
files as safe for program and file delivery.
GroupWritableIncludeFile
Allow group writable
:include:
files.
GroupWritableIncludeFileSafe
Accept group-writable
:include:
files as safe for program and file delivery.
GroupWritableSASLDBFile
Accept a group-writable Cyrus SASL password file.
HelpFileInUnsafeDirPath
Allow the file named in the
HelpFile
option to be in an unsafe directory.
IncludeFileInGroupWritableDirPath
Allow
:include:
files in group writable directories.
IncludeFileInUnsafeDirPath
Allow
:include:
files in unsafe directories.
IncludeFileInUnsafeDirPathSafe
Allow a
:include:
file that is in an unsafe directory to include references to program and files.
InsufficientEntropy
Try to use STARTTLS even if the PRNG for OpenSSL is not properly seeded despite the secu-
rity problems.
LinkedAliasFileInWritableDir
Allow an alias file that is a link in a writable directory.
LinkedClassFileInWritableDir
Allow class files that are links in writable directories.
LinkedForwardFileInWritableDir
Allow
.forward
files that are links in writable directories.
LinkedIncludeFileInWritableDir
Allow
:include:
files that are links in writable directories.
LinkedMapInWritableDir
Allow map files that are links in writable directories. This includes alias database files.
LinkedServiceSwitchFileInWritableDir
Allow the service switch file to be a link even if the directory is writable.
MapInUnsafeDirPath
Allow maps (e.g.,
hash
,
btree
, and
dbm
files) in unsafe directories. This includes alias database
files.
SMM:08-34 Sendmail Installation and Operation Guide
NonRootSafeAddr
Do not mark file and program deliveries as unsafe if sendmail is not running with root privi-
leges.
RunProgramInUnsafeDirPath
Run programs that are in writable directories without logging a warning.
RunWritableProgram
Run programs that are group- or world-writable without logging a warning.
TrustStickyBit
Allow group or world writable directories if the sticky bit is set on the directory. Do not set this
on systems which do not honor the sticky bit on directories.
WorldWritableAliasFile
Accept world-writable alias files.
WorldWritableForwardfile
Allow world writable
.forward
files.
WorldWritableIncludefile
Allow world writable
:include:
files.
WriteMapToHardLink
Allow writes to maps that are hard links.
WriteMapToSymLink
Allow writes to maps that are symbolic links.
WriteStatsToHardLink
Allow the status file to be a hard link.
WriteStatsToSymLink
Allow the status file to be a symbolic link.
4.10. Connection Caching
When processing the queue,
sendmail
will try to keep the last few open connections open to avoid
startup and shutdown costs. This only applies to IPC and LPC connections.
When trying to open a connection the cache is first searched. If an open connection is found, it is
probed to see if it is still active by sending a
RSET
command. It is not an error if this fails; instead, the con-
nection is closed and reopened.
Tw o parameters control the connection cache. The
ConnectionCacheSize
(
k
) option defines the num-
ber of simultaneous open connections that will be permitted. If it is set to zero, connections will be closed as
quickly as possible. The default is one. This should be set as appropriate for your system size; it will limit
the amount of system resources that
sendmail
will use during queue runs. Never set this higher than 4.
The
ConnectionCacheTimeout
(
K
) option specifies the maximum time that any cached connection
will be permitted to idle. When the idle time exceeds this value the connection is closed. This number
should be small (under ten minutes) to prevent you from grabbing too many resources from other hosts. The
default is five minutes.
4.11. Name Server Access
Control of host address lookups is set by the
hosts
service entry in your service switch file. If you are
on a system that has built-in service switch support (e.g., Ultrix, Solaris, or DEC OSF/1) then your system is
probably configured properly already. Otherwise,
sendmail
will consult the file
/etc/mail/service.switch
,
which should be created.
Sendmail
only uses two entries:
hosts
and
aliases
, although system routines may
use other services (notably the
passwd
service for user name lookups by
getpwname
).
Sendmail Installation and Operation Guide
SMM:08-35
However, some systems (such as SunOS 4.X) will do DNS lookups regardless of the setting of the ser-
vice switch entry. In particular, the system routine
gethostbyname
(3) is used to look up host names, and
many vendor versions try some combination of DNS, NIS, and file lookup in /etc/hosts without consulting a
service switch.
Sendmail
makes no attempt to work around this problem, and the DNS lookup will be done
anyway. If you do not have a nameserver configured at all, such as at a UUCP-only site,
sendmail
will get a
“connection refused” message when it tries to connect to the name server. If the
hosts
switch entry has the
service “dns” listed somewhere in the list,
sendmail
will interpret this to mean a temporary failure and will
queue the mail for later processing; otherwise, it ignores the name server data.
The same technique is used to decide whether to do MX lookups. If you want MX support, you
must
have “dns” listed as a service in the
hosts
switch entry.
The
ResolverOptions
(
I
) option allows you to tweak name server options. The command line takes a
series of flags as documented in
resolver
(3) (with the leading “RES_” deleted). Each can be preceded by an
optional ‘+’ or ‘
−
’. For example, the line
O ResolverOptions=+AAONLY
−
DNSRCH
turns on the AAONLY (accept authoritative answers only) and turns off the DNSRCH (search the domain
path) options. Most resolver libraries default DNSRCH, DEFNAMES, and RECURSE flags on and all oth-
ers off. If NETINET6 is enabled, most libraries default to USE_INET6 as well. You can also include
“HasWildcardMX” to specify that there is a wildcard MX record matching your domain; this turns off MX
matching when canonifying names, which can lead to inappropriate canonifications. Use “WorkAroundBro-
kenAAAA” when faced with a broken nameserver that returns SERVFAIL (a temporary failure) on
T_AAAA (IPv6) lookups during hostname canonification. Notice: it might be necessary to apply the same
(or similar) options to
submit.cf
too.
Version level 1 configurations (see the section about ‘‘Configuration Version Level’’) turn DNSRCH
and DEFNAMES off when doing delivery lookups, but leave them on everywhere else. Version 8 of
send-
ignores them when doing canonification lookups (that is, when using $[ ... $]), and always does the
search. If you don’t want to do automatic name extension, don’t call $[ ... $].
The search rules for $[ ... $] are somewhat different than usual. If the name being looked up has at
least one dot, it always tries the unmodified name first. If that fails, it tries the reduced search path, and lastly
tries the unmodified name (but only for names without a dot, since names with a dot have already been tried).
This allows names such as ‘‘utc.CS’’ to match the site in Czechoslovakia rather than the site in your local
Computer Science department. It also prefers A and CNAME records over MX records — that is, if it finds
an MX record it makes note of it, but keeps looking. This way, if you have a wildcard MX record matching
your domain, it will not assume that all names match.
To completely turn off all name server access on systems without service switch support (such as
SunOS 4.X) you will have to recompile with −DNAMED_BIND=0 and remove −lresolv from the list of li-
braries to be searched when linking.
4.12. Moving the Per-User Forward Files
Some sites mount each user’s home directory from a local disk on their workstation, so that local ac-
cess is fast. However, the result is that .forward file lookups from a central mail server are slow. In some
cases, mail can even be delivered on machines inappropriately because of a file server being down. The per-
formance can be especially bad if you run the automounter.
The
ForwardPath
(
J
) option allows you to set a path of forward files. For example, the config file
line
O ForwardPath=/var/forward/$u:$z/.forward.$w
would first look for a file with the same name as the user’s login in /var/forward; if that is not found (or is in-
accessible) the file ‘‘.forward.
machinename
’’ in the user’s home directory is searched. A truly perverse site
could also search by sender by using $r, $s, or $f.
SMM:08-36 Sendmail Installation and Operation Guide
If you create a directory such as /var/forward, it should be mode 1777 (that is, the sticky bit should be
set). Users should create the files mode 0644. Note that you must use the ForwardFileInUnsafeDirPath and
ForwardFileInUnsafeDirPathSafe flags with the
DontBlameSendmail
option to allow forward files in a
world writable directory. This might also be used as a denial of service attack (users could create forward
files for other users); a better approach might be to create /var/forward mode 0755 and create empty files for
each user, owned by that user, mode 0644. If you do this, you don’t hav e to set the DontBlameSendmail op-
tions indicated above.
4.13. Free Space
On systems that have one of the system calls in the
statfs
(2) family (including
statvfs
and
ustat
), you
can specify a minimum number of free blocks on the queue filesystem using the
MinFreeBlocks
(
b
) option.
If there are fewer than the indicated number of blocks free on the filesystem on which the queue is mounted
the SMTP server will reject mail with the 452 error code. This invites the SMTP client to try again later.
Beware of setting this option too high; it can cause rejection of email when that mail would be
processed without difficulty.
4.14. Maximum Message Size
To avoid overflowing your system with a large message, the
MaxMessageSize
option can be set to set
an absolute limit on the size of any one message. This will be advertised in the ESMTP dialogue and
checked during message collection.
4.15. Privacy Flags
The
PrivacyOptions
(
p
) option allows you to set certain ‘‘privacy’’ flags. Actually, many of them
don’t giv e you any extra privacy, rather just insisting that client SMTP servers use the HELO command be-
fore using certain commands or adding extra headers to indicate possible spoof attempts.
The option takes a series of flag names; the final privacy is the inclusive or of those flags. For exam-
ple:
O PrivacyOptions=needmailhelo, noexpn
insists that the HELO or EHLO command be used before a MAIL command is accepted and disables the
EXPN command.
The flags are detailed in section 5.6.
4.16. Send to Me Too
Beginning with version 8.10,
sendmail
includes by default the (envelope) sender in any list expan-
sions. For example, if “matt” sends to a list that contains “matt” as one of the members he will get a copy of
the message. If the
MeToo
option is set to
FALSE
(in the configuration file or via the command line), this be-
havior is changed, i.e., the (envelope) sender is excluded in list expansions.
5. THE WHOLE SCOOP ON THE CONFIGURATION FILE
This section describes the configuration file in detail.
There is one point that should be made clear immediately: the syntax of the configuration file is designed
to be reasonably easy to parse, since this is done every time
sendmail
starts up, rather than easy for a human to
read or write. The configuration file should be generated via the method described in
cf/README
, it should
not be edited directly unless someone is familiar with the internals of the syntax described here and it is not pos-
sible to achieve the desired result via the default method.
The configuration file is organized as a series of lines, each of which begins with a single character defin-
ing the semantics for the rest of the line. Lines beginning with a space or a tab are continuation lines (although
the semantics are not well defined in many places). Blank lines and lines beginning with a sharp symbol (‘#’)
are comments.
Sendmail Installation and Operation Guide
SMM:08-37
5.1. R and S — Rewriting Rules
The core of address parsing are the rewriting rules. These are an ordered production system.
Send-
scans through the set of rewriting rules looking for a match on the left hand side (LHS) of the rule.
When a rule matches, the address is replaced by the right hand side (RHS) of the rule.
There are several sets of rewriting rules. Some of the rewriting sets are used internally and must have
specific semantics. Other rewriting sets do not have specifically assigned semantics, and may be referenced
by the mailer definitions or by other rewriting sets.
The syntax of these two commands are:
S
n
Sets the current ruleset being collected to
n
. If you begin a ruleset more than once it appends to the old defi-
nition.
R
lhs rhs comments
The fields must be separated by at least one tab character; there may be embedded spaces in the fields. The
lhs
is a pattern that is applied to the input. If it matches, the input is rewritten to the
rhs
. The
comments
are
ignored.
Macro expansions of the form
$
x
are performed when the configuration file is read. A literal
$
can be
included using
$$
. Expansions of the form
$&
x
are performed at run time using a somewhat less general al-
gorithm. This is intended only for referencing internally defined macros such as
$h
that are changed at run-
time.
5.1.1. The left hand side
The left hand side of rewriting rules contains a pattern. Normal words are simply matched directly.
Metasyntax is introduced using a dollar sign. The metasymbols are:
$*
Match zero or more tokens
$+
Match one or more tokens
$−
Match exactly one token
$=
x
Match any phrase in class
x
$˜
x
Match any word not in class
x
If any of these match, they are assigned to the symbol
$
n
for replacement on the right hand side, where
n
is the index in the LHS. For example, if the LHS:
$−:$+
is applied to the input:
UCBARPA:eric
the rule will match, and the values passed to the RHS will be:
$1 UCBARPA
$2 eric
Additionally, the LHS can include
$@
to match zero tokens. This is
not
bound to a
$
n
on the
RHS, and is normally only used when it stands alone in order to match the null input.
5.1.2. The right hand side
When the left hand side of a rewriting rule matches, the input is deleted and replaced by the right
hand side. Tokens are copied directly from the RHS unless they begin with a dollar sign. Metasymbols
are:
SMM:08-38 Sendmail Installation and Operation Guide
$
n
Substitute indefinite token
n
from LHS
$[
name
$]
Canonicalize
name
$(
map key
$@
arguments
$:
default
$)
Generalized keyed mapping function
$>
n
“Call” ruleset
n
$#
mailer
Resolve to
mailer
$@
host
Specify
host
$:
user
Specify
user
The
$
n
syntax substitutes the corresponding value from a
$+
,
$−
,
$*
,
$=
, or
$˜
match on the LHS.
It may be used anywhere.
A host name enclosed between
$[
and
$]
is looked up in the host database(s) and replaced by the
canonical name
14
.
For example, “$[ftp$]” might become “ftp.CS.Berkeley.EDU” and
“$[[128.32.130.2]$]” would become “vangogh.CS.Berkeley.EDU.”
Sendmail
recognizes its numeric IP
address without calling the name server and replaces it with its canonical name.
The
$(
...
$)
syntax is a more general form of lookup; it uses a named map instead of an implicit
map. If no lookup is found, the indicated
default
is inserted; if no default is specified and no lookup
matches, the value is left unchanged. The
arguments
are passed to the map for possible use.
The
$>
n
syntax causes the remainder of the line to be substituted as usual and then passed as the
argument to ruleset
n
. The final value of ruleset
n
then becomes the substitution for this rule. The
$>
syntax expands everything after the ruleset name to the end of the replacement string and then passes that
as the initial input to the ruleset. Recursive calls are allowed. For example,
$>0 $>3 $1
expands $1, passes that to ruleset 3, and then passes the result of ruleset 3 to ruleset 0.
The
$#
syntax should
only
be used in ruleset zero, a subroutine of ruleset zero, or rulesets that re-
turn decisions (e.g., check_rcpt). It causes evaluation of the ruleset to terminate immediately, and signals
to
sendmail
that the address has completely resolved. The complete syntax for ruleset 0 is:
$#
mailer
$@
host
$:
user
This specifies the {mailer, host, user} 3-tuple (triple) necessary to direct the mailer. Note: the third ele-
ment (
user
) is often also called
address
part. If the mailer is local the host part may be omitted
15
. The
mailer
must be a single word, but the
host
and
user
may be multi-part. If the
mailer
is the built-in IPC
mailer, the
host
may be a colon (or comma) separated list of hosts. Each is separately MX expanded and
the results are concatenated to make (essentially) one long MX list. Hosts separated by a comma have
the same MX preference, and for each colon separated host the MX preference is increased. The
user
is
later rewritten by the mailer-specific envelope rewriting set and assigned to the
$u
macro. As a special
case, if the mailer specified has the
F=@
flag specified and the first character of the
$:
value is “@”, the
“@” is stripped off, and a flag is set in the address descriptor that causes sendmail to not do ruleset 5 pro-
cessing.
Normally, a rule that matches is retried, that is, the rule loops until it fails. A RHS may also be
preceded by a
$@
or a
$:
to change this behavior. A
$@
prefix causes the ruleset to return with the re-
mainder of the RHS as the value. A
$:
prefix causes the rule to terminate immediately, but the ruleset to
continue; this can be used to avoid continued application of a rule. The prefix is stripped before continu-
ing.
14
This is actually completely equivalent to $(host
hostname
$). In particular, a
$:
default can be used.
15
You may want to use it for special “per user” extensions. For example, in the address “jgm+foo@CMU.EDU”; the “+foo” part is not part
of the user name, and is passed to the local mailer for local use.
Sendmail Installation and Operation Guide
SMM:08-39
The
$@
and
$:
prefixes may precede a
$>
spec; for example:
R$+ $: $>7 $1
matches anything, passes that to ruleset seven, and continues; the
$:
is necessary to avoid an infinite loop.
Substitution occurs in the order described, that is, parameters from the LHS are substituted, host-
names are canonicalized, “subroutines” are called, and finally
$#
,
$@
, and
$:
are processed.
5.1.3. Semantics of rewriting rule sets
There are six rewriting sets that have specific semantics. Five of these are related as depicted by
figure 1.
Ruleset three should turn the address into “canonical form.” This form should have the basic syn-
tax:
local-part@host-domain-spec
Ruleset three is applied by
sendmail
before doing anything with any address.
If no “@” sign is specified, then the host-domain-spec
may
be appended (box “D” in Figure 1)
from the sender address (if the
C
flag is set in the mailer definition corresponding to the
sending
mailer).
Ruleset zero is applied after ruleset three to addresses that are going to actually specify recipients.
It must resolve to a
{mailer, host, address}
triple. The
mailer
must be defined in the mailer definitions
addr
3
D
1
S
2
R
4
msg
0
resolved address
Figure 1 — Rewriting set semantics
D — sender domain addition
S — mailer-specific sender rewriting
R — mailer-specific recipient rewriting
SMM:08-40 Sendmail Installation and Operation Guide
from the configuration file. The
host
is defined into the
$h
macro for use in the argv expansion of the
specified mailer. Notice: since the envelope sender address will be used if a delivery status notification
must be send, i.e., it may specify a recipient, it is also run through ruleset zero. If ruleset zero returns a
temporary error
4xy
then delivery is deferred. This can be used to temporarily disable delivery, e.g.,
based on the time of the day or other varying parameters. It should not be used to quarantine e-mails.
Rulesets one and two are applied to all sender and recipient addresses respectively. They are ap-
plied before any specification in the mailer definition. They must never resolve.
Ruleset four is applied to all addresses in the message. It is typically used to translate internal to
external form.
In addition, ruleset 5 is applied to all local addresses (specifically, those that resolve to a mailer
with the ‘F=5’ flag set) that do not have aliases. This allows a last minute hook for local names.
5.1.4. Ruleset hooks
A few extra rulesets are defined as “hooks” that can be defined to get special features. They are all
named rulesets. The “check_*” forms all give accept/reject status; falling off the end or returning nor-
mally is an accept, and resolving to
$#error
is a reject or quarantine. Quarantining is chosen by specify-
ing
quarantine
in the second part of the mailer triple:
$#error $@ quarantine $: Reason for quarantine
Many of these can also resolve to the special mailer name
$#discard
; this accepts the message as though
it were successful but then discards it without delivery. Note, this mailer cannot be chosen as a mailer in
ruleset 0. Note also that all “check_*” rulesets have to deal with temporary failures, especially for map
lookups, themselves, i.e., they should return a temporary error code or at least they should make a proper
decision in those cases.
5.1.4.1. check_relay
The
check_relay
ruleset is called after a connection is accepted by the daemon. It is not called
when sendmail is started using the
−bs
option. It is passed
client.host.name $| client.host.address
where
$|
is a metacharacter separating the two parts. This ruleset can reject connections from various
locations. Note that it only checks the connecting SMTP client IP address and hostname. It does not
check for third party message relaying. The
check_rcpt
ruleset discussed below usually does third
party message relay checking.
5.1.4.2. check_mail
The
check_mail
ruleset is passed the user name parameter of the
SMTP MAIL
command. It can
accept or reject the address.
5.1.4.3. check_rcpt
The
check_rcpt
ruleset is passed the user name parameter of the
SMTP RCPT
command. It can
accept or reject the address.
5.1.4.4. check_data
The
check_data
ruleset is called after the
SMTP DAT A
command, its parameter is the number of
recipients. It can accept or reject the command.
5.1.4.5. check_other
The
check_other
ruleset is invoked for all unknown SMTP commands and for commands
which do not have specific rulesets, e.g., NOOP and VERB. Internal checks, e.g., those explained in
Sendmail Installation and Operation Guide
SMM:08-41
"Measures against Denial of Service Attacks", are performed first. The ruleset is passed
entire-SMTP-command $| SMTP-reply-first-digit
where
$|
is a metacharacter separating the two parts. For example,
VERB $| 2
reflects receiving the "VERB" SMTP command and the intent to return a "2XX" SMTP success reply.
Alternatively,
JUNK TYPE=I $| 5
reflects receiving the unknown "JUNK TYPE=I" SMTP command and the intent to return a "5XX"
SMTP failure reply. If the ruleset returns the SMTP reply code 421:
$#error $@ 4.7.0 $: 421 bad command
the session is terminated. Note: it is a bad idea to return the original command in the error text to the
client as that might be abused for certain attacks. The ruleset cannot override a rejection triggered by
the built-in rules.
5.1.4.6. check_compat
The
check_compat
ruleset is passed
sender-address $| recipient-address
where
$|
is a metacharacter separating the addresses. It can accept or reject mail transfer between
these two addresses much like the
checkcompat()
function. Note: while other
check_*
rulesets are in-
voked during the SMTP mail reception stage (i.e., in the SMTP server),
check_compat
is invoked
during the mail delivery stage.
5.1.4.7. check_eoh
The
check_eoh
ruleset is passed
number-of-headers $| size-of-headers
where
$|
is a metacharacter separating the numbers. These numbers can be used for size comparisons
with the
arith
map. The ruleset is triggered after all of the headers have been read. It can be used to
correlate information gathered from those headers using the
macro
storage map. One possible use is
to check for a missing header. For example:
SMM:08-42 Sendmail Installation and Operation Guide
Kstorage macro
HMessage-Id: $>CheckMessageId
SCheckMessageId
# Record the presence of the header
R$* $: $(storage {MessageIdCheck} $@ OK $) $1
R< $+ @ $+ >
$@ OK
R$* $#error $: 553 Header Error
Scheck_eoh
# Check the macro
R$* $: < $&{MessageIdCheck} >
# Clear the macro for the next message
R$* $: $(storage {MessageIdCheck} $) $1
# Has a Message-Id: header
R< $+ >
$@ OK
# Allow missing Message-Id: from local mail
R$* $: < $&{client_name} >
R< >
$@ OK
R< $=w >
$@ OK
# Otherwise, reject the mail
R$* $#error $: 553 Header Error
Keep in mind the Message-Id: header is not a required header and is not a guaranteed spam indicator.
This ruleset is an example and should probably not be used in production.
5.1.4.8. check_eom
The
check_eom
ruleset is called after the end of a message, its parameter is the message size. It
can accept or reject the message.
5.1.4.9. check_etrn
The
check_etrn
ruleset is passed the parameter of the
SMTP ETRN
command. It can accept or
reject the command.
5.1.4.10. check_expn
The
check_expn
ruleset is passed the user name parameter of the
SMTP EXPN
command. It can
accept or reject the address.
5.1.4.11. check_vrfy
The
check_vrfy
ruleset is passed the user name parameter of the
SMTP VRFY
command. It can
accept or reject the command.
5.1.4.12. clt_features
The
clt_features
ruleset is called with the server’s host name before sendmail connects to it
(only if sendmail is compiled with STARTTLS or SASL). This ruleset should return
$#
followed by
a list of options (in general, single characters delimited by white space). If the return value starts
with anything else it is silently ignored. Generally upper case characters turn off a feature while
lower case characters turn it on. The options are copied into
${client_flags}
thus overriding any ex-
isting flags. Option ‘D’ causes the client to not use DANE, which is useful to interact with MTAs
that have a broken DANE setup by simply not using it. Note: The
d
option in
tls_clt_features
to turn
off DANE does not work when the server does not even offer STARTTLS.
Sendmail Installation and Operation Guide
SMM:08-43
5.1.4.13. trust_auth
The
trust_auth
ruleset is passed the AUTH= parameter of the
SMTP MAIL
command. It is used
to determine whether this value should be trusted. In order to make this decision, the ruleset may
make use of the various
${auth_*}
macros. If the ruleset does resolve to the “error” mailer the
AUTH= parameter is not trusted and hence not passed on to the next relay.
5.1.4.14. tls_client
The
tls_client
ruleset is called when sendmail acts as server: after a STARTTLS command has
been issued and the TLS handshake was performed, and from
check_mail.
The parameter is the value
of
${verify}
and STARTTLS or MAIL, respectively. If the ruleset does resolve to the “error” mailer,
the appropriate error code is returned to the client, for STARTTLS this happens for (most) subsequent
commands.
5.1.4.15. tls_server
The
tls_server
ruleset is called when sendmail acts as client after a STARTTLS command
(should) have been issued. The parameter is the value of
${verify}
. If the ruleset does resolve to the
“error” mailer, the connection is aborted (treated as non-deliverable with a permanent or temporary
error).
5.1.4.16. tls_rcpt
The
tls_rcpt
ruleset is called each time before a RCPT command is sent. The parameter is the
current recipient. If the ruleset does resolve to the “error” mailer, the RCPT command is suppressed
(treated as non-deliverable with a permanent or temporary error). This ruleset allows to require en-
cryption or verification of the recipient’s MTA even if the mail is somehow redirected to another host.
For example, sending mail to
luke@endmail.org
may get redirected to a host named
death.star
and
hence the tls_server ruleset won’t apply. By introducing per recipient restrictions such attacks (e.g.,
via DNS spoofing) can be made impossible. See
cf/README
how this ruleset can be used.
5.1.4.17. srv_features
The
srv_features
ruleset is called with the connecting client’s host name when a client connects
to sendmail. This ruleset should return
$#
followed by a list of options (in general, single characters
delimited by white space). If the return value starts with anything else it is silently ignored. Gener-
ally upper case characters turn off a feature while lower case characters turn it on. Option ‘S’ causes
the server not to offer STARTTLS, which is useful to interact with MTAs/MUAs that have broken
STARTTLS implementations by simply not offering it. ‘V’ turns off the request for a client certifi-
cate during the TLS handshake. Options ‘A’ and ‘P’ suppress SMTP AUTH and PIPELINING, re-
spectively. ‘c’ is the equivalent to AuthOptions=p, i.e., it doesn’t permit mechanisms susceptible to
simple passive attack (e.g., PLAIN, LOGIN), unless a security layer is active. Option ‘l’ requires
SMTP AUTH for a connection. Options ’B’, ’D’, ’E’, and ’X’ suppress SMTP VERB, DSN, ETRN,
and EXPN, respectively. If a client sends one of the (HTTP) commands GET, POST, CONNECT, or
USER the connection is immediately terminated in the following cases: if sent as first command, if
sent as first command after STARTTLS, or if the ’h’ option is set. Option ’F’ disables SMTP transac-
tion stuffing protection which is enabled by default. The protection checks for clients which try to
send commands without waiting for the server HELO/EHLO and DAT A response. For an SMTP
message, the option ’o’ causes the server to accept only CRLF as end of line and only CRLF . CRLF
as end of a message as required by the RFCs. The latter is also a defense against SMTP smuggling
(CVE-2023-51765). Option ’O’ allows the server to accept a single dot on a line by itself as end of
an SMTP message (and LF as end of line). Option ’g’ instructs the server to fail SMTP messages
which have a LF without a CR directly before it ("bare LF") by dropping the session with a 421 error.
Option ’G’ accepts SMTP messages which have a "bare LF". Option ’u’ instructs the server to fail
SMTP messages which have a CR without a LF directly after it ("bare CR") by dropping the session
SMM:08-44 Sendmail Installation and Operation Guide
with a 421 error. Option ’U’ accepts SMTP messages which have a "bare CR". There is a variant for
the options ’u’ and ’g’: a ’2’ can be appended to the single character, in which case the server will re-
place the offending bare CR or bare LF with a space. This allows to accept mail from broken sys-
tems, but the message is modified to avoid SMTP smuggling. If needed, systems with broken SMTP
implementations can be allowed some violations, e.g., a combination of
G U g2 u2 O
A command like
egrep ’Bare.*(CR|LF).*not allowed’ $MAILLOG
can be used to find hosts which send bare CR or LF.
A
Do not offer AUTH
a
Offer AUTH (default)
B
Do not offer VERB
b
Offer VERB (default)
C
Do not require security layer for
plaintext AUTH (default)
c
Require security layer for plaintext AUTH
D
Do not offer DSN
d
Offer DSN (default)
E
Do not offer ETRN
e
Offer ETRN (default)
F
Disable transaction stuffing protection
f
Enforce transaction stuffing protection (default)
G
Accept "bare LF"s in a message
g
Do not accept "bare LF"s in a message (default)
g2 Replace "bare LF" in a message with space
h
Terminate session after HTTP commands
L
Do not require AUTH (default)
l
Require AUTH
O
Do not require CRLF as end of line in an SMTP message
o
Require CRLF as end of line in an SMTP message (default)
P
Do not offer PIPELINING
p
Offer PIPELINING (default)
S
Do not offer STARTTLS
s
Offer STARTTLS (default)
U
Accept "bare CR"s in a message
u
Do not accept "bare CR"s in a message (default)
u2 Replace "bare CR" in a message with space
V
Do not request a client certificate
v
Request a client certificate (default)
X
Do not offer EXPN
x
Offer EXPN (default)
Note: the entries marked as ‘‘(default)’’ may require that some configuration has been made, e.g.,
SMTP AUTH is only available if properly configured. Moreover, many options can be changed on a
global basis via other settings as explained in this document, e.g., via DaemonPortOptions.
The ruleset may return ‘$#temp’ to indicate that there is a temporary problem determining the
correct features, e.g., if a map is unavailable. In that case, the SMTP server issues a temporary failure
and does not accept email.
Sendmail Installation and Operation Guide
SMM:08-45
5.1.4.18. try_tls
The
try_tls
ruleset is called when sendmail connects to another MTA. The argument for the
ruleset is the name of the server. If the ruleset does resolve to the “error” mailer, sendmail does not
try STARTTLS even if it is offered. This is useful to deal with STARTTLS interoperability issues by
simply not using it.
5.1.4.19. tls_srv_features and tls_clt_features
The
tls_clt_features
ruleset is called right before sendmail issues the
STARTTLS
command to
another MTA and the
tls_srv_features
ruleset is called when a client sends the
STARTTLS
command
to
sendmail
. The arguments for the rulesets are the host name and IP address of the other side sepa-
rated by
$|
(which is a metacharacter). They should return a list of
key=value
pairs separated by
semicolons; the list can be empty if no options should be applied to the connection. Av ailable keys
are and their allowed values are:
Options
A comma separated list of SSL related options. See
ServerSSLOptions
and
ClientSSLOptions
for
details, as well as
SSL_set_options
(3) and note this warning: Options already set before are not
cleared!
CipherList
Specify cipher list for STARTTLS (does not apply to TLSv1.3), see
ciphers
(1) for possible val-
ues. This overrides the global
CipherList
for the session.
CipherSuites
Specify cipher suites for STARTTLS TLSv1.3 (depends on TLS library support). This overrides
the global
CipherSuites
for the session.
CertFile
File containing a certificate.
Ke yFile
File containing the private key for the certificate.
Flags
Currently the only valid flags are
R
to require a CRL for each encountered certificate during verification (by default a missing CRL
is ignored),
c
and
C
which basically clears/sets the option
TLSFallbacktoClear
for just this session, respec-
tively,
d
to turn off DANE which is obviously only valid for
tls_clt_features
and requires DANE to be
compiled in. This might be needed in case of a misconfiguration, e.g., specifying invalid TLSA
RRs.
Example:
Stls_srv_features
R$* $| 10.$+
$: cipherlist=HIGH
Notes:
Errors in these features (e.g., unknown keys or inv alid values) are logged. Additionally, to
avoid using STARTTLS with features that should have been changed, the following happens: for
tls_clt_features
the session is aborted, i.e., no e-mail is sent, and for
tls_srv_features
a temporary er-
ror is returned in reply to the
STARTTLS
command.
The keys are case-insensitive.
Both
CertFile
and
Ke yFile
must be specified together; specifying only one is an error.
SMM:08-46 Sendmail Installation and Operation Guide
5.1.4.20. authinfo
The
authinfo
ruleset is called when sendmail tries to authenticate to another MTA. The argu-
ments for the ruleset are the host name and IP address of the server separated by
$|
(which is a
metacharacter). It should return
$#
followed by a list of tokens that are used for SMTP AUTH. If the
return value starts with anything else it is silently ignored. Each token is a tagged string of the form:
"TDstring" (including the quotes), where
T
Tag which describes the item
D
Delimiter: ’:’ simple text follows
’=’ string is base64 encoded
string Value of the item
Valid values for the tag are:
U
user (authorization) id
I
authentication id
P
password
R
realm
M
list of mechanisms delimited by spaces
If this ruleset is defined, the option
DefaultAuthInfo
is ignored (even if the ruleset does not return a
‘‘useful’’ result).
5.1.4.21. queuegroup
The
queuegroup
ruleset is used to map a recipient address to a queue group name. The input
for the ruleset is the recipient address (i.e., the address part of the resolved triple) The ruleset should
return
$#
followed by the name of a queue group. If the return value starts with anything else it is
silently ignored. See the section about ‘‘Queue Groups and Queue Directories’’ for further informa-
tion.
5.1.4.22. greet_pause
The
greet_pause
ruleset is used to specify the amount of time to pause before sending the ini-
tial SMTP 220 greeting. The arguments for the ruleset are the host name and IP address of the client
separated by
$|
(which is a metacharacter). If any traffic is received during that pause, an SMTP 554
rejection response is given instead of the 220 greeting and all SMTP commands are rejected during
that connection. This helps protect sites from open proxies and SMTP slammers. The ruleset should
return
$#
followed by the number of milliseconds (thousandths of a second) to pause. If the return
value starts with anything else or is not a number, it is silently ignored. Note: this ruleset is not in-
voked (and hence the feature is disabled) when smtps (SMTP over SSL) is used, i.e., the
s
modifier is
set for the daemon via
DaemonPortOptions
, because in this case the SSL handshake is performed
before the greeting is sent.
5.1.5. IPC mailers
Some special processing occurs if the ruleset zero resolves to an IPC mailer (that is, a mailer that
has “[IPC]” listed as the Path in the
M
configuration line. The host name passed after “$@” has MX ex-
pansion performed if not delivering via a named socket; this looks the name up in DNS to find alternate
delivery sites.
The host name can also be provided as a dotted quad or an IPv6 address in square brackets; for ex-
ample:
[128.32.149.78]
or
[IPv6:2002:c0a8:51d2::23f4]
Sendmail Installation and Operation Guide
SMM:08-47
This causes direct conversion of the numeric value to an IP host address.
The host name passed in after the “$@” may also be a colon or comma separated list of hosts.
Each is separately MX expanded and the results are concatenated to make (essentially) one long MX list.
Hosts separated by a comma have the same MX preference, and for each colon separated host the MX
preference is increased. The intent here is to create “fake” MX records that are not published in DNS for
private internal networks.
As a final special case, the host name can be passed in as a text string in square brackets:
[ucbvax.berkeley.edu]
This form avoids the MX mapping.
N.B.:
This is intended only for situations where you have a network
firewall or other host that will do special processing for all your mail, so that your MX record points to a
gateway machine; this machine could then do direct delivery to machines within your local domain. Use
of this feature directly violates RFC 1123 section 5.3.5: it should not be used lightly.
5.2. D — Define Macro
Macros are named with a single character or with a word in {braces}. The names ‘‘x’’ and ‘‘{x}’’ de-
note the same macro for every single character ‘‘x’’. Single character names may be selected from the entire
ASCII set, but user-defined macros should be selected from the set of upper case letters only. Lower case let-
ters and special symbols are used internally. Long names beginning with a lower case letter or a punctuation
character are reserved for use by sendmail, so user-defined long macro names should begin with an upper
case letter.
The syntax for macro definitions is:
D
x val
where
x
is the name of the macro (which may be a single character or a word in braces) and
val
is the value
it should have. There should be no spaces given that do not actually belong in the macro value.
Macros are interpolated using the construct
$
x
, where
x
is the name of the macro to be interpolated.
This interpolation is done when the configuration file is read, except in
M
lines. The special construct
$&
x
can be used in
R
lines to get deferred interpolation.
Conditionals can be specified using the syntax:
$?x text1 $| text2 $.
This interpolates
text1
if the macro
$x
is set and non-null, and
text2
otherwise. The “else” (
$|
) clause may be
omitted.
The following macros are defined and/or used internally by
sendmail
for interpolation into argv’s for
mailers or for other contexts. The ones marked † are information passed into sendmail
16
, the ones marked ‡
are information passed both in and out of sendmail, and the unmarked macros are passed out of sendmail but
are not otherwise used internally. These macros are:
$a The origination date in RFC 822 format. This is extracted from the Date: line.
$b The current date in RFC 822 format.
$c The hop count. This is a count of the number of Received: lines plus the value of the
−h
command
line flag.
$d The current date in UNIX (ctime) format.
$e† (Obsolete; use SmtpGreetingMessage option instead.) The SMTP entry message. This is printed out
when SMTP starts up. The first word must be the
$j
macro as specified by RFC 821. Defaults to “$j
Sendmail $v ready at $b”. Commonly redefined to include the configuration version number, e.g., “$j
16
As of version 8.6, all of these macros have reasonable defaults. Previous versions required that they be defined.
SMM:08-48 Sendmail Installation and Operation Guide
Sendmail $v/$Z ready at $b”
$f The envelope sender (from) address.
$g The sender address relative to the recipient. For example, if
$f
is “foo”,
$g
will be “host!foo”,
“foo@host.domain”, or whatever is appropriate for the receiving mailer.
$h The recipient host. This is set in ruleset 0 from the $@ field of a parsed address.
$i The queue id, e.g., “f344MXxp018717”.
$j‡ The “official” domain name for this site. This is fully qualified if the full qualification can be found. It
must
be redefined to be the fully qualified domain name if your system is not configured so that infor-
mation can find it automatically.
$k The UUCP node name (from the uname system call).
$l† (Obsolete; use UnixFromLine option instead.) The format of the UNIX from line. Unless you have
changed the UNIX mailbox format, you should not change the default, which is “From $g $d”.
$m The domain part of the
gethostname
return value. Under normal circumstances,
$j
is equivalent to
$w.$m
.
$n† The name of the daemon (for error messages). Defaults to “MAILER-DAEMON”.
$o† (Obsolete: use OperatorChars option instead.) The set of “operators” in addresses. A list of characters
which will be considered tokens and which will separate tokens when doing parsing. For example, if
“@” were in the
$o
macro, then the input “a@b” would be scanned as three tokens: “a,” “@,” and “b.”
Defaults to “.:@[]”, which is the minimum set necessary to do RFC 822 parsing; a richer set of opera-
tors is “.:%@!/[]”, which adds support for UUCP, the %-hack, and X.400 addresses.
$p Sendmail’s process id.
$r Protocol used to receive the message. Set from the
−p
command line flag or by the SMTP server code.
$s Sender’s host name. Set from the
−p
command line flag or by the SMTP server code (in which case it
is set to the EHLO/HELO parameter).
$t A numeric representation of the current time in the format YYYYMMDDHHmm (4 digit year
1900-9999, 2 digit month 01-12, 2 digit day 01-31, 2 digit hours 00-23, 2 digit minutes 00-59).
$u The recipient user.
$v The version number of the
sendmail
binary.
$w‡ The hostname of this site. This is the root name of this host (but see below for caveats).
$x The full name of the sender.
$z The home directory of the recipient.
$_ The validated sender host name (see below for details).
${addr_type}
The type of the address which is currently being rewritten. This macro contains up to three characters,
the first is either ‘e’ or ‘h’ for envelope/header address, the second is a space, and the third is either ‘s’
or ‘r’ for sender/recipient address.
${alg_bits}
The maximum keylength (in bits) of the symmetric encryption algorithm used for a TLS connection.
This may be less than the effective keylength, which is stored in
${cipher_bits}
, for ‘‘export con-
trolled’’ algorithms.
${auth_authen}
The client’s authentication credentials as determined by authentication (only set if successful). The
format depends on the mechanism used, it might be just ‘user’, or ‘user@realm’, or something similar
(SMTP AUTH only).
Sendmail Installation and Operation Guide
SMM:08-49
${auth_author}
The authorization identity, i.e. the AUTH= parameter of the
SMTP MAIL
command if supplied.
${auth_type}
The mechanism used for SMTP authentication (only set if successful).
${auth_ssf}
The keylength (in bits) of the symmetric encryption algorithm used for the security layer of a SASL
mechanism.
${bodytype}
The message body type (7BIT or 8BITMIME), as determined from the envelope.
${cert_fp}
The fingerprint of the presented certificate (STARTTLS only). Note: this macro is only defined if the
option
CertFingerprintAlgorithm
is set, in which case the specified fingerprint algorithm is used.
The valid algorithms depend on the OpenSSL version, but usually md5, sha1, and sha256 are avail-
able. See
openssl dgst -h
for a list.
${cert_issuer}
The DN (distinguished name) of the CA (certificate authority) that signed the presented certificate (the
cert issuer) (STARTTLS only).
${cert_md5}
The MD5 hash of the presented certificate (STARTTLS only). Note: this macro is only defined if the
option
CertFingerprintAlgorithm
is not set.
${cert_subject}
The DN of the presented certificate (called the cert subject) (STARTTLS only).
${cipher}
The cipher suite used for the connection, e.g., EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC-
SHA, DES-CBC-MD5, DES-CBC3-SHA (STARTTLS only).
${cipher_bits}
The effective keylength (in bits) of the symmetric encryption algorithm used for a TLS connection.
${client_addr}
The IP address of the SMTP client. IPv6 addresses are tagged with "IPv6:" before the address. De-
fined in the SMTP server only.
${client_connections}
The number of open connections in the SMTP server for the client IP address.
${client_flags}
The flags specified by the Modifier= part of
ClientPortOptions
where flags are separated from each
other by spaces and upper case flags are doubled. That is, Modifier=hA will be represented as "h AA"
in
${client_flags}
, which is required for testing the flags in rulesets.
${client_name}
The host name of the SMTP client. This may be the client’s bracketed IP address in the form [
nnn.nnn.nnn.nnn ] for IPv4 and [ IPv6:nnnn:...:nnnn ] for IPv6 if the client’s IP address is not resolv-
able, or if it is resolvable but the IP address of the resolved hostname doesn’t match the original IP ad-
dress. Defined in the SMTP server only. See also
${client_resolve}
.
${client_port}
The port number of the SMTP client. Defined in the SMTP server only.
${client_ptr}
The result of the PTR lookup for the client IP address. Note: this is the same as
${client_name}
if and
SMM:08-50 Sendmail Installation and Operation Guide
only if
${client_resolve}
is OK. Defined in the SMTP server only.
${client_rate}
The number of incoming connections for the client IP address over the time interval specified by Con-
nectionRateWindowSize.
${client_resolve}
Holds the result of the resolve call for
${client_name}
. Possible values are:
OK resolved successfully
FAIL permanent lookup failure
FORGED forward lookup doesn’t match reverse lookup
TEMP temporary lookup failure
Defined in the SMTP server only.
sendmail
performs a hostname lookup on the IP address of the con-
necting client. Next the IP addresses of that hostname are looked up. If the client IP address does not
appear in that list, then the hostname is maybe forged. This is reflected as the value FORGED for
${client_resolve}
and it also shows up in
$_
as "(may be forged)".
${cn_issuer}
The CN (common name) of the CA that signed the presented certificate (STARTTLS only). Note: if
the CN cannot be extracted properly it will be replaced by one of these strings based on the encoun-
tered error:
BadCertificateContainsNUL CN contains a NUL character
BadCertificateTooLong CN is too long
BadCertificateUnknown CN could not be extracted
In the last case, some other (unspecific) error occurred.
${cn_subject}
The CN (common name) of the presented certificate (STARTTLS only). See
${cn_issuer}
for possible
replacements.
${currHeader}
Header value as quoted string (possibly truncated to
MAXNAME
). This macro is only available in
header check rulesets.
${daemon_addr}
The IP address the daemon is listening on for connections.
${daemon_family}
The network family if the daemon is accepting network connections. Possible values include “inet”,
“inet6”, “iso”, “ns”, “x.25”
${daemon_flags}
The flags for the daemon as specified by the Modifier= part of
DaemonPortOptions
whereby the flags
are separated from each other by spaces, and upper case flags are doubled. That is, Modifier=Ea will
be represented as "EE a" in
${daemon_flags}
, which is required for testing the flags in rulesets.
${daemon_info}
Some information about a daemon as a text string. For example, “SMTP+queueing@00:30:00”.
${daemon_name}
The name of the daemon from
DaemonPortOptions
Name= suboption. If this suboption is not set,
"Daemon#", where # is the daemon number, is used.
${daemon_port}
The port the daemon is accepting connection on. Unless
DaemonPortOptions
is set, this will most
likely be “25”.
${deliveryMode}
The current delivery mode sendmail is using. It is initially set to the value of the
DeliveryMode
Sendmail Installation and Operation Guide
SMM:08-51
option.
${dsn_envid}
The envelope id parameter (ENVID=) passed to sendmail as part of the envelope.
${dsn_notify}
Value of DSN NOTIFY= parameter (never, success, failure, delay, or empty string).
${dsn_ret}
Value of DSN RET= parameter (hdrs, full, or empty string).
${envid}
The envelope id parameter (ENVID=) passed to sendmail as part of the envelope.
${hdrlen}
The length of the header value which is stored in ${currHeader} (before possible truncation). If this
value is greater than or equal to
MAXNAME
the header has been truncated.
${hdr_name}
The name of the header field for which the current header check ruleset has been called. This is useful
for a default header check ruleset to get the name of the header; the macro is only available in header
check rulesets.
${if_addr}
The IP address of the interface of an incoming connection unless it is in the loopback net. IPv6 ad-
dresses are tagged with "IPv6:" before the address.
${if_addr_out}
The IP address of the interface of an outgoing connection unless it is in the loopback net. IPv6 ad-
dresses are tagged with "IPv6:" before the address.
${if_family}
The IP family of the interface of an incoming connection unless it is in the loopback net.
${if_family_out}
The IP family of the interface of an outgoing connection unless it is in the loopback net.
${if_name}
The hostname associated with the interface of an incoming connection. This macro can be used for
SmtpGreetingMessage and HReceived for virtual hosting. For example:
O SmtpGreetingMessage=$?{if_name}${if_name}$|$j$. MTA
${if_name_out}
The hostname associated with the interface of an outgoing connection.
${load_avg}
The current load average.
${mail_addr}
The address part of the resolved triple of the address given for the
SMTP MAIL
command. Defined in
the SMTP server only.
${mail_host}
The host from the resolved triple of the address given for the
SMTP MAIL
command. Defined in the
SMTP server only.
${mail_mailer}
The mailer from the resolved triple of the address given for the
SMTP MAIL
command. Defined in the
SMTP server only.
${msg_id}
The value of the Message-Id: header.
SMM:08-52 Sendmail Installation and Operation Guide
${msg_size}
The value of the SIZE= parameter, i.e., usually the size of the message (in an ESMTP dialogue), be-
fore the message has been collected, thereafter the message size as computed by
sendmail
(and can be
used in check_compat).
${nbadrcpts}
The number of bad recipients for a single message.
${nrcpts}
The number of validated recipients for a single message. Note: since recipient validation happens after
check_rcpt
has been called, the value in this ruleset is one less than what might be expected.
${ntries}
The number of delivery attempts.
${opMode}
The current operation mode (from the
−b
flag).
${quarantine}
The quarantine reason for the envelope, if it is quarantined.
${queue_interval}
The queue run interval given by the
−q
flag. For example,
−q30m
would set
${queue_interval}
to
“00:30:00”.
${rcpt_addr}
The address part of the resolved triple of the address given for the
SMTP RCPT
command. Defined in
the SMTP server only after a RCPT command.
${rcpt_host}
The host from the resolved triple of the address given for the
SMTP RCPT
command. Defined in the
SMTP server only after a RCPT command.
${rcpt_mailer}
The mailer from the resolved triple of the address given for the
SMTP RCPT
command. Defined in the
SMTP server only after a RCPT command.
${server_addr}
The address of the server of the current outgoing SMTP connection. For LMTP delivery the macro is
set to the name of the mailer. (only if sendmail is compiled with STARTTLS or SASL.)
${server_name}
The name of the server of the current outgoing SMTP or LMTP connection. (only if sendmail is com-
piled with STARTTLS or SASL.)
${time}
The output of the
time
(3) function, i.e., the number of seconds since 0 hours, 0 minutes, 0 seconds,
January 1, 1970, Coordinated Universal Time (UTC).
${tls_version}
The TLS/SSL version used for the connection, e.g., TLSv1.2, TLSv1; defined after STARTTLS has
been used.
${total_rate}
The total number of incoming connections over the time interval specified by ConnectionRateWindow-
Size.
${verify}
The result of the verification of the presented cert; only defined after STARTTLS has been used (or at-
tempted). Possible values are:
Sendmail Installation and Operation Guide
SMM:08-53
TRUSTED verification via DANE succeeded.
DANE_FAIL verification via DANE failed.
DANE_TEMP verification via DANE failed temporarily.
DANE_NOTLS DANE required but STARTTLS was not available.
OK verification succeeded.
NO no cert presented.
NOT
no cert requested.
FAIL cert presented but could not be verified,
e.g., the signing CA is missing.
NONE STARTTLS has not been performed.
CLEAR STARTTLS has been disabled internally
for a clear text delivery attempt.
TEMP temporary error occurred.
PROT OCOL some protocol error occurred
at the ESMTP level (not TLS).
CONFIG tls_*_features failed due to a syntax error.
SOFTWARE STARTTLS handshake failed,
which is a fatal error for this session,
the e-mail will be queued.
There are three types of dates that can be used. The
$a
and
$b
macros are in RFC 822 format;
$a
is
the time as extracted from the “Date:” line of the message (if there was one), and
$b
is the current date and
time (used for postmarks). If no “Date:” line is found in the incoming message,
$a
is set to the current time
also. The
$d
macro is equivalent to the
$b
macro in UNIX (ctime) format.
The macros
$w
,
$j
, and
$m
are set to the identity of this host.
Sendmail
tries to find the fully qualified
name of the host if at all possible; it does this by calling
gethostname
(2) to get the current hostname and then
passing that to
gethostbyname
(3) which is supposed to return the canonical version of that host name.
17
As-
suming this is successful,
$j
is set to the fully qualified name and
$m
is set to the domain part of the name
(everything after the first dot). The
$w
macro is set to the first word (everything before the first dot) if you
have a lev el 5 or higher configuration file; otherwise, it is set to the same value as
$j
. If the canonification is
not successful, it is imperative that the config file set
$j
to the fully qualified domain name
18
.
The
$f
macro is the id of the sender as originally determined; when mailing to a specific host the
$g
macro is set to the address of the sender
relative to the recipient.
For example, if I send to “bollard@ma-
tisse.CS.Berkeley.EDU” from the machine “vangogh.CS.Berkeley.EDU” the
$f
macro will be “eric” and the
$g
macro will be “eric@vangogh.CS.Berkeley.EDU.”
The
$x
macro is set to the full name of the sender. This can be determined in several ways. It can be
passed as flag to
sendmail
. It can be defined in the
NAME
environment variable. The third choice is the
value of the “Full-Name:” line in the header if it exists, and the fourth choice is the comment field of a
“From:” line. If all of these fail, and if the message is being originated locally, the full name is looked up in
the
/etc/passwd
file.
When sending, the
$h
,
$u
, and
$z
macros get set to the host, user, and home directory (if local) of the
recipient. The first two are set from the
$@
and
$:
part of the rewriting rules, respectively.
The
$p
and
$t
macros are used to create unique strings (e.g., for the “Message-Id:” field). The
$i
macro is set to the queue id on this host; if put into the timestamp line it can be extremely useful for tracking
messages. The
$v
macro is set to be the version number of
sendmail
; this is normally put in timestamps and
has been proven extremely useful for debugging.
17
For example, on some systems
gethostname
might return “foo” which would be mapped to “foo.bar.com” by
gethostbyname
.
18
Older versions of sendmail didn’t pre-define
$j
at all, so up until 8.6, config files
always
had to define
$j
.
SMM:08-54 Sendmail Installation and Operation Guide
The
$c
field is set to the “hop count,” i.e., the number of times this message has been processed. This
can be determined by the
−h
flag on the command line or by counting the timestamps in the message.
The
$r
and
$s
fields are set to the protocol used to communicate with
sendmail
and the sending host-
name. They can be set together using the
−p
command line flag or separately using the
−M
or
−oM
flags.
The
$_
macro is set to a validated sender host name. If the sender is running an RFC 1413 compliant
IDENT server and the receiver has the IDENT protocol turned on, it will include the user name on that host.
The
${client_name}
,
${client_addr}
, and
${client_port}
macros are set to the name, address, and port
number of the SMTP client who is invoking
sendmail
as a server. These can be used in the
check_*
rulesets
(using the
$&
deferred evaluation form, of course!).
5.3. C and F — Define Classes
Classes of phrases may be defined to match on the left hand side of rewriting rules, where a “phrase” is
a sequence of characters that does not contain space characters. For example a class of all local names for
this site might be created so that attempts to send to oneself can be eliminated. These can either be defined
directly in the configuration file or read in from another file. Classes are named as a single letter or a word in
{braces}. Class names beginning with lower case letters and special characters are reserved for system use.
Classes defined in config files may be given names from the set of upper case letters for short names or be-
ginning with an upper case letter for long names.
The syntax is:
C
c phrase1 phrase2...
F
c file
F
c |program
F
c [mapkey]@mapclass:mapspec
The first form defines the class
c
to match any of the named words. If
phrase1
or
phrase2
is another class,
e.g.,
$=S
, the contents of class
S
are added to class
c
. It is permissible to split them among multiple lines;
for example, the two forms:
CHmonet ucbmonet
and
CHmonet
CHucbmonet
are equivalent. The ‘‘F’’ forms read the elements of the class
c
from the named
file
,
program
, or
map speci-
fication
. Each element should be listed on a separate line. To specify an optional file, use ‘‘−o’’ between the
class name and the file name, e.g.,
Fc −o /path/to/file
If the file can’t be used,
sendmail
will not complain but silently ignore it. The map form should be an op-
tional map key, an at sign, and a map class followed by the specification for that map. Examples include:
F{VirtHosts}@ldap:−k (&(objectClass=virtHosts)(host=*)) −v host
F{MyClass}foo@hash:/etc/mail/classes
will fill the class
$={VirtHosts}
from an LDAP map lookup and
$={MyClass}
from a hash database map
lookup of the key
foo
. There is also a built-in schema that can be accessed by only specifying:
F{
ClassName
}@LDAP
This will tell sendmail to use the default schema:
Sendmail Installation and Operation Guide
SMM:08-55
−k (&(objectClass=sendmailMTAClass)
(sendmailMTAClassName=
ClassName
)
(|(sendmailMTACluster=${sendmailMTACluster})
(sendmailMTAHost=$j)))
−v sendmailMTAClassValue
Note that the lookup is only done when sendmail is initially started.
Elements of classes can be accessed in rules using
$=
or
$˜
. The
$˜
(match entries not in class) only
matches a single word; multi-word entries in the class are ignored in this context.
Some classes have internal meaning to
sendmail
:
$=e contains the Content-Transfer-Encodings that can be 8
→
7 bit encoded. It is predefined to contain
“7bit”, “8bit”, and “binary”.
$=k set to be the same as
$k
, that is, the UUCP node name.
$=m set to the set of domains by which this host is known, initially just
$m
.
$=n can be set to the set of MIME body types that can never be eight to seven bit encoded. It defaults to
“multipart/signed”. Message types “message/*” and “multipart/*” are never encoded directly. Mul-
tipart messages are always handled recursively. The handling of message/* messages are controlled
by class
$=s
.
$=q A set of Content-Types that will never be encoded as base64 (if they hav e to be encoded, they will
be encoded as quoted-printable). It can have primary types (e.g., “text”) or full types (such as
“text/plain”).
$=s contains the set of subtypes of message that can be treated recursively. By default it contains only
“rfc822”. Other “message/*” types cannot be 8
→
7 bit encoded. If a message containing eight bit
data is sent to a seven bit host, and that message cannot be encoded into seven bits, it will be
stripped to 7 bits.
$=t set to the set of trusted users by the
T
configuration line. If you want to read trusted users from a
file, use
Ft
/file/name
.
$=w set to be the set of all names this host is known by. This can be used to match local hostnames.
$={persistentMacros}
set to the macros that should be saved across queue runs. Care should be taken when adding macro
names to this class.
Sendmail
can be compiled to allow a
scanf
(3) string on the
F
line. This lets you do simplistic parsing
of text files. For example, to read all the user names in your system
/etc/passwd
file into a class, use
FL/etc/passwd %[ˆ:]
which reads every line up to the first colon.
5.4. E — Set or Propagate Environment Variables
E
configuration lines set or propagate environment variables into children.
E
name
will propagate the named variable from the environment when
sendmail
was inv oked into any children it
calls;
E
name
=
value
sets the named variable to the indicated value. Any variables not explicitly named will not be in the child en-
vironment.
SMM:08-56 Sendmail Installation and Operation Guide
5.5. M — Define Mailer
Programs and interfaces to mailers are defined in this line. The format is:
M
name
, {
field
=
value
}*
where
name
is the name of the mailer (used internally only) and the “field=name” pairs define attributes of
the mailer. Fields are:
Path The pathname of the mailer
Flags Special flags for this mailer
Sender Rewriting set(s) for sender addresses
Recipient Rewriting set(s) for recipient addresses
recipients Maximum number of recipients per envelope
Argv An argument vector to pass to this mailer
Eol The end-of-line string for this mailer
Maxsize The maximum message length to this mailer
maxmessages The maximum message deliveries per connection
Linelimit The maximum line length in the message body
Directory The working directory for the mailer
Userid The default user and group id to run as
Nice The nice(2) increment for the mailer
Charset The default character set for 8-bit characters
Type Type information for DSN diagnostics
Wait The maximum time to wait for the mailer
Queuegroup The default queue group for the mailer
/
The root directory for the mailer
Only the first character of the field name is checked (it’s case-sensitive).
The following flags may be set in the mailer description. Any other flags may be used freely to condi-
tionally assign headers to messages destined for particular mailers. Flags marked with † are not interpreted
by the
sendmail
binary; these are the conventionally used to correlate to the flags portion of the
H
line. Flags
marked with ‡ apply to the mailers for the sender address rather than the usual recipient mailers.
a
Run Extended SMTP (ESMTP) protocol (defined in RFCs 1869, 1652, and 1870). This flag defaults on
if the SMTP greeting message includes the word “ESMTP”.
A
Look up the user (address) part of the resolved mailer triple, in the alias database. Normally this is only
set for local mailers.
b
Force a blank line on the end of a message. This is intended to work around some stupid versions of
/bin/mail that require a blank line, but do not provide it themselves. It would not normally be used on
network mail.
B
Strip leading backslashes (\) off of the address; this is a subset of the functionality of the
s
flag.
c
Do not include comments in addresses. This should only be used if you have to work around a remote
mailer that gets confused by comments. This strips addresses of the form “Phrase <address>” or “ad-
dress (Comment)” down to just “address”.
C‡ If mail is
received
from a mailer with this flag set, any addresses in the header that do not have an at
sign (“@”) after being rewritten by ruleset three will have the “@domain” clause from the sender enve-
lope address tacked on. This allows mail with headers of the form:
From: usera@hosta
To: userb@hostb, userc
to be rewritten as:
From: usera@hosta
To: userb@hostb, userc@hosta
Sendmail Installation and Operation Guide
SMM:08-57
automatically. Howev er, it doesn’t really work reliably.
d
Do not include angle brackets around route-address syntax addresses. This is useful on mailers that are
going to pass addresses to a shell that might interpret angle brackets as I/O redirection. However, it
does not protect against other shell metacharacters. Therefore, passing addresses to a shell should not
be considered secure.
D† This mailer wants a “Date:” header line.
e
This mailer is expensive to connect to, so try to avoid connecting normally; any necessary connection
will occur during a queue run. See also option
HoldExpensive
.
E
Escape lines beginning with “From ” in the message with a ‘>’ sign.
f
The mailer wants a
−f
from
flag, but only if this is a network forward operation (i.e., the mailer will
give an error if the executing user does not have special permissions).
F† This mailer wants a “From:” header line.
g
Normally,
sendmail
sends internally generated email (e.g., error messages) using the null return address
as required by RFC 1123. However, some mailers don’t accept a null return address. If necessary, you
can set the
g
flag to prevent
sendmail
from obeying the standards; error messages will be sent as from
the MAILER-DAEMON (actually, the value of the
$n
macro).
h
Upper case should be preserved in host names (the $@ portion of the mailer triple resolved from ruleset
0) for this mailer.
i
Do User Database rewriting on envelope sender address.
I
This flag is deprecated and will be removed from a future version. This mailer will be speaking SMTP
to another
sendmail
— as such it can use special protocol features. This flag should not be used except
for debugging purposes because it uses
VERB
as SMTP command.
j
Do User Database rewriting on recipients as well as senders.
k
Normally when
sendmail
connects to a host via SMTP, it checks to make sure that this isn’t accidentally
the same host name as might happen if
sendmail
is misconfigured or if a long-haul network interface is
set in loopback mode. This flag disables the loopback check. It should only be used under very unusual
circumstances.
K
Currently unimplemented. Reserved for chunking.
l
This mailer is local (i.e., final delivery will be performed).
L
Limit the line lengths as specified in RFC 821. This deprecated option should be replaced by the
L=
mail declaration. For historic reasons, the
L
flag also sets the
7
flag.
m
This mailer can send to multiple users on the same host in one transaction. When a
$u
macro occurs in
the
argv
part of the mailer definition, that field will be repeated as necessary for all qualifying users.
Removing this flag can defeat duplicate suppression on a remote site as each recipient is sent in a sepa-
rate transaction.
M† This mailer wants a “Message-Id:” header line.
n
Do not insert a UNIX-style “From” line on the front of the message.
o
Always run as the owner of the recipient mailbox. Normally
sendmail
runs as the sender for locally
generated mail or as “daemon” (actually, the user specified in the
u
option) when delivering network
mail. The normal behavior is required by most local mailers, which will not allow the envelope sender
address to be set unless the mailer is running as daemon. This flag is ignored if the
S
flag is set.
p
Use the route-addr style reverse-path in the SMTP
SMTP MAIL
command rather than just the return ad-
dress; although this is required in RFC 821 section 3.1, many hosts do not process reverse-paths prop-
erly. Rev erse-paths are officially discouraged by RFC 1123.
P† This mailer wants a “Return-Path:” line.
SMM:08-58 Sendmail Installation and Operation Guide
q
When an address that resolves to this mailer is verified (SMTP VRFY command), generate 250 re-
sponses instead of 252 responses. This will imply that the address is local.
r
Same as
f
, but sends a
−r
flag.
R
Open SMTP connections from a “secure” port. Secure ports aren’t (secure, that is) except on UNIX
machines, so it is unclear that this adds anything.
sendmail
must be running as root to be able to use
this flag.
s
Strip quote characters (" and \) off of the address before calling the mailer.
S
Don’t reset the userid before calling the mailer. This would be used in a secure environment where
sendmail
ran as root. This could be used to avoid forged addresses. If the
U=
field is also specified,
this flag causes the effective user id to be set to that user.
u
Upper case should be preserved in user names for this mailer. Standards require preservation of case in
the local part of addresses, except for those address for which your system accepts responsibility. RFC
2142 provides a long list of addresses which should be case insensitive. If you use this flag, you may be
violating RFC 2142. Note that postmaster is always treated as a case insensitive address regardless of
this flag.
U
This mailer wants UUCP-style “From” lines with the ugly “remote from <host>” on the end.
w
The user must have a valid account on this machine, i.e.,
getpwnam
(3) must succeed. If not, the mail is
bounced. See also the
MailboxDatabase
option. This is required to get “.forward” capability.
W
Ignore long term host status information (see Section "Persistent Host Status Information").
x† This mailer wants a “Full-Name:” header line.
X
This mailer wants to use the hidden dot algorithm as specified in RFC 821; basically, any line beginning
with a dot will have an extra dot prepended (to be stripped at the other end). This insures that lines in
the message containing a dot will not terminate the message prematurely.
z
Run Local Mail Transfer Protocol (LMTP) between
sendmail
and the local mailer. This is a variant on
SMTP defined in RFC 2033 that is specifically designed for delivery to a local mailbox.
Z
Apply DialDelay (if set) to this mailer.
0
Don’t look up MX records for hosts sent via SMTP/LMTP. Do not apply
FallbackMXhost
either.
1
Strip null characters (’\0’) when sending to this mailer.
2
Don’t use ESMTP even if offered; this is useful for broken systems that offer ESMTP but fail on EHLO
(without recovering when HELO is tried next).
3
Extend the list of characters converted to =XX notation when converting to Quoted-Printable to include
those that don’t map cleanly between ASCII and EBCDIC. Useful if you have IBM mainframes on site.
5
If no aliases are found for this address, pass the address through ruleset 5 for possible alternate resolu-
tion. This is intended to forward the mail to an alternate delivery spot.
6
Strip headers to seven bits.
7
Strip all output to seven bits. This is the default if the
L
flag is set. Note that clearing this option is not
sufficient to get full eight bit data passed through
sendmail
. If the
7
option is set, this is essentially al-
ways set, since the eighth bit was stripped on input. Note that this option will only impact messages
that didn’t hav e 8
→
7 bit MIME conversions performed.
8
If set, it is acceptable to send eight bit data to this mailer; the usual attempt to do 8
→
7 bit MIME con-
versions will be bypassed.
9
If set, do
limited
7
→
8 bit MIME conversions. These conversions are limited to text/plain data.
:
Check addresses to see if they begin with “:include:”; if they do, convert them to the “*include*” mailer.
|
Check addresses to see if they begin with a ‘|’; if they do, convert them to the “prog” mailer.
Sendmail Installation and Operation Guide
SMM:08-59
/
Check addresses to see if they begin with a ‘/’; if they do, convert them to the “*file*” mailer.
@
Look up addresses in the user database.
%
Do not attempt delivery on initial receipt of a message or on queue runs unless the queued message is
selected using one of the -qI/-qR/-qS queue run modifiers or an ETRN request.
!
Disable an MH hack that drops an explicit From: header if it is the same as what sendmail would gener-
ate.
Configuration files prior to level 6 assume the ‘A’, ‘w’, ‘5’, ‘:’, ‘|’, ‘/’, and ‘@’ options on the mailer
named “local”.
The mailer with the special name “error” can be used to generate a user error. The (optional) host field
is an exit status to be returned, and the user field is a message to be printed. The exit status may be numeric
or one of the values USAGE, NOUSER, NOHOST, UNAVAILABLE, SOFTWARE, TEMPFAIL, PROT O-
COL, or CONFIG to return the corresponding EX_ exit code, or an enhanced error code as described in RFC
1893,
Enhanced Mail System Status Codes.
For example, the entry:
$#error $@ NOHOST $: Host unknown in this domain
on the RHS of a rule will cause the specified error to be generated and the “Host unknown” exit status to be
returned if the LHS matches. This mailer is only functional in rulesets 0, 5, or one of the check_* rulesets.
The host field can also contain the special token
quarantine
which instructs sendmail to quarantine the cur-
rent message.
The mailer with the special name “discard” causes any mail sent to it to be discarded but otherwise
treated as though it were successfully delivered. This mailer cannot be used in ruleset 0, only in the various
address checking rulesets.
The mailer named “local”
must
be defined in every configuration file. This is used to deliver local
mail, and is treated specially in several ways. Additionally, three other mailers named “prog”, “*file*”, and
“*include*” may be defined to tune the delivery of messages to programs, files, and :include: lists respec-
tively. They default to:
Mprog, P=/bin/sh, F=lsoDq9, T=DNS/RFC822/X-Unix, A=sh −c $u
M*file*, P=[FILE], F=lsDFMPEouq9, T=DNS/RFC822/X-Unix, A=FILE $u
M*include*, P=/dev/null, F=su, A=INCLUDE $u
Builtin pathnames are [FILE] and [IPC], the former is used for delivery to files, the latter for delivery
via interprocess communication. For mailers that use [IPC] as pathname the argument vector (A=) must start
with TCP or FILE for delivery via a TCP or a Unix domain socket. If TCP is used, the second argument
must be the name of the host to contact. Optionally a third argument can be used to specify a port, the de-
fault is smtp (port 25). If FILE is used, the second argument must be the name of the Unix domain socket.
If the argument vector does not contain $u then
sendmail
will speak SMTP (or LMTP if the mailer flag
z is specified) to the mailer.
If no Eol field is defined, then the default is "\r\n" for SMTP mailers and "\n" for others.
The Sender and Recipient rewriting sets may either be a simple ruleset id or may be two ids separated
by a slash; if so, the first rewriting set is applied to envelope addresses and the second is applied to headers.
Setting any value to zero disables corresponding mailer-specific rewriting.
The Directory is actually a colon-separated path of directories to try. For example, the definition
“D=$z:/” first tries to execute in the recipient’s home directory; if that is not available, it tries to execute in
the root of the filesystem. This is intended to be used only on the “prog” mailer, since some shells (such as
csh
) refuse to execute if they cannot read the current directory. Since the queue directory is not normally
readable by unprivileged users
csh
scripts as recipients can fail.
The Userid specifies the default user and group id to run as, overriding the
DefaultUser
option (q.v.).
If the
S
mailer flag is also specified, this user and group will be set as the effective uid and gid for the
process. This may be given as
user:group
to set both the user and group id; either may be an integer or a
SMM:08-60 Sendmail Installation and Operation Guide
symbolic name to be looked up in the
passwd
and
group
files respectively. If only a symbolic user name is
specified, the group id in the
passwd
file for that user is used as the group id.
The Charset field is used when converting a message to MIME; this is the character set used in the
Content-Type: header. If this is not set, the
DefaultCharSet
option is used, and if that is not set, the value
“unknown-8bit” is used.
WARNING:
this field applies to the sender’s mailer, not the recipient’s mailer. For
example, if the envelope sender address lists an address on the local network and the recipient is on an exter-
nal network, the character set will be set from the Charset= field for the local network mailer, not that of the
external network mailer.
The Type= field sets the type information used in MIME error messages as defined by RFC 1894. It is
actually three values separated by slashes: the MTA-type (that is, the description of how hosts are named),
the address type (the description of e-mail addresses), and the diagnostic type (the description of error diag-
nostic codes). Each of these must be a registered value or begin with “X−”. The default is
“dns/rfc822/smtp”.
The m= field specifies the maximum number of messages to attempt to deliver on a single SMTP or
LMTP connection. The default is infinite.
The r= field specifies the maximum number of recipients to attempt to deliver in a single envelope. It
defaults to 100.
The /= field specifies a new root directory for the mailer. The path is macro expanded and then passed
to the “chroot” system call. The root directory is changed before the Directory field is consulted or the uid is
changed.
The Wait= field specifies the maximum time to wait for the mailer to return after sending all data to it.
This applies to mailers that have been forked by
sendmail
.
The Queuegroup= field specifies the default queue group in which received mail should be queued.
This can be overridden by other means as explained in section ‘‘Queue Groups and Queue Directories’’.
5.6. H — Define Header
The format of the header lines that
sendmail
inserts into the message are defined by the
H
line. The
syntax of this line is one of the following:
H
hname
:
htemplate
H
[
?
mflags
?]
hname
:
htemplate
H
[
?$
{macro}
?]
hname
:
htemplate
Continuation lines in this spec are reflected directly into the outgoing message. The
htemplate
is macro-ex-
panded before insertion into the message. If the
mflags
(surrounded by question marks) are specified, at least
one of the specified flags must be stated in the mailer definition for this header to be automatically output. If
a
${macro}
(surrounded by question marks) is specified, the header will be automatically output if the macro
is set. The macro may be set using any of the normal methods, including using the
macro
storage map in a
ruleset. If one of these headers is in the input it is reflected to the output regardless of these flags or macros.
Notice: If a
${macro}
is used to set a header, then it is useful to add that macro to class
$={persistent-
Macros}
which consists of the macros that should be saved across queue runs.
Some headers have special semantics that will be described later.
A secondary syntax allows validation of headers as they are being read. To enable validation, use:
H
Header
: $>
Ruleset
H
Header
: $>+
Ruleset
The indicated
Ruleset
is called for the specified
Header
, and can return
$#error
to reject or quarantine the
message or
$#discard
to discard the message (as with the other
check_
* rulesets). The ruleset receives the
header field-body as argument, i.e., not the header field-name; see also ${hdr_name} and ${currHeader}.
The header is treated as a structured field, that is, text in parentheses is deleted before processing, unless the
Sendmail Installation and Operation Guide
SMM:08-61
second form
$>+
is used. Note: only one ruleset can be associated with a header;
sendmail
will silently ig-
nore multiple entries.
For example, the configuration lines:
HMessage-Id: $>CheckMessageId
SCheckMessageId
R< $+ @ $+ >
$@ OK
R$* $#error $: Illegal Message-Id header
would refuse any message that had a Message-Id: header of any of the following forms:
Message-Id: <>
Message-Id: some text
Message-Id: <legal text@domain> extra crud
A default ruleset that is called for headers which don’t hav e a specific ruleset defined for them can be speci-
fied by:
H
*
: $>
Ruleset
or
H
*
: $>+
Ruleset
5.7. O — Set Option
There are a number of global options that can be set from a configuration file. Options are represented
by full words; some are also representable as single characters for back compatibility. The syntax of this line
is:
O
option
=
value
This sets option
option
to be
value
. Note that there
must
be a space between the letter ‘O’ and the name of
the option. An older version is:
O
o value
where the option
o
is a single character. Depending on the option,
value
may be a string, an integer, a
boolean (with legal values “t”, “T”, “f”, or “F”; the default is TRUE), or a time interval.
All filenames used in options should be absolute paths, i.e., starting with ’/’. Relative filenames most
likely cause surprises during operation (unless otherwise noted).
The options supported (with the old, one character names in brackets) are:
AliasFile=
spec, spec, ...
[A] Specify possible alias file(s). Each
spec
should be in the format ‘‘
class
:
info
’’ where
class
:
is optional and defaults to ‘‘implicit’’. Note that
info
is required for all
class
es ex-
cept “ldap”. For the “ldap” class, if
info
is not specified, a default
info
value is used as fol-
lows:
−k (&(objectClass=sendmailMTAAliasObject)
(sendmailMTAAliasName=aliases)
(|(sendmailMTACluster=${sendmailMTACluster})
(sendmailMTAHost=$j))
(sendmailMTAKey=%0))
−v sendmailMTAAliasValue
Depending on how
sendmail
is compiled, valid classes are “implicit” (search through a
compiled-in list of alias file types, for back compatibility), “hash” (if
NEWDB
is specified),
“btree” (if
NEWDB
is specified), “dbm” (if
NDBM
is specified), “cdb” (if
CDB
is specified),
“stab” (internal symbol table — not normally used unless you have no other database
SMM:08-62 Sendmail Installation and Operation Guide
lookup), “sequence” (use a sequence of maps previously declared), “ldap” (if
LDAPMAP
is
specified), or “nis” (if
NIS
is specified). If a list of
spec
s are provided,
sendmail
searches
them in order.
AliasWait=
timeout
[a] If set, wait up to
timeout
(units default to minutes) for an “@:@” entry to exist in the
alias database before starting up. If it does not appear in the
timeout
interval issue a warn-
ing.
AllowBogusHELO
If set, allow HELO SMTP commands that don’t include a host name. Setting this violates
RFC 1123 section 5.2.5, but is necessary to interoperate with several SMTP clients. If
there is a value, it is still checked for legitimacy.
AuthMaxBits=
N
Limit the maximum encryption strength for the security layer in SMTP AUTH (SASL).
Default is essentially unlimited. This allows to turn off additional encryption in SASL if
STARTTLS is already encrypting the communication, because the existing encryption
strength is taken into account when choosing an algorithm for the security layer. For ex-
ample, if STARTTLS is used and the symmetric cipher is 3DES, then the keylength (in
bits) is 168. Hence setting
AuthMaxBits
to 168 will disable any encryption in SASL.
AuthMechanisms List of authentication mechanisms for AUTH (separated by spaces). The advertised list of
authentication mechanisms will be the intersection of this list and the list of available
mechanisms as determined by the Cyrus SASL library. If STARTTLS is active, EXTER-
NAL will be added to this list. In that case, the value of {cert_subject} is used as authenti-
cation id provided
${verify}
is
OK
.
AuthOptions List of options for SMTP AUTH consisting of single characters with intervening white
space or commas.
A
Use the AUTH= parameter for the MAIL
command only when authentication succeeded.
This can be used as a workaround for broken
MTAs that do not implement RFC 2554 correctly.
a
protection from active (non-dictionary) attacks
during authentication exchange.
c
require mechanisms which pass client credentials,
and allow mechanisms which can pass credentials
to do so.
d
don’t permit mechanisms susceptible to passive
dictionary attack.
f
require forward secrecy between sessions
(breaking one won’t help break next).
m
require mechanisms which provide mutual authentication
(only available if using Cyrus SASL v2 or later).
p
don’t permit mechanisms susceptible to simple
passive attack (e.g., PLAIN, LOGIN), unless a
security layer is active.
y
don’t permit mechanisms that allow anonymous login.
The first option applies to sendmail as a client, the others to a server. Example:
O AuthOptions=p,y
would disallow ANONYMOUS as AUTH mechanism and would allow PLAIN and LO-
GIN only if a security layer (e.g., provided by STARTTLS) is already active. The options
’a’, ’c’, ’d’, ’f’, ’p’, and ’y’ refer to properties of the selected SASL mechanisms. Expla-
nations of these properties can be found in the Cyrus SASL documentation.
Sendmail Installation and Operation Guide
SMM:08-63
AuthRealm The authentication realm that is passed to the Cyrus SASL library. If no realm is specified,
$j
is used. See also KNOWNBUGS.
BadRcptThrottle=
N
If set and the specified number of recipients in a single SMTP transaction have been re-
jected, sleep for one second after each subsequent RCPT command in that transaction.
BlankSub=
c
[B] Set the blank substitution character to
c
. Unquoted spaces in addresses are replaced by
this character. Defaults to space (i.e., no change is made).
CACertPath Path to directory with certificates of CAs. This directory directory must contain the hashes
of each CA certificate as filenames (or as links to them).
CACertFile File containing one or more CA certificates; see section about STARTTLS for more infor-
mation.
CertFingerprintAlgorithm
Specify the fingerprint algorithm (digest) to use for the presented cert. If the option is not
set, md5 is used and the macro
${cert_md5}
contains the cert fingerprint. If the option is
explicitly set, the specified algorithm (e.g., sha1) is used and the macro
${cert_fp}
contains
the cert fingerprint.
CipherList Specify cipher list for STARTTLS (does not apply to TLSv1.3). See
ciphers
(1) for possi-
ble values.
CipherSuites Specify cipher suites for STARTTLS TLSv1.3 (depends on TLS library support). See
SSL_CTX_set_ciphersuites
(3) for possible values.
CheckAliases [n] Validate the RHS of aliases when rebuilding the alias database.
CheckpointInterval=
N
[C] Checkpoints the queue every
N
(default 10) addresses sent. If your system crashes
during delivery to a large list, this prevents retransmission to any but the last
N
recipients.
ClassFactor=
fact
[z] The indicated
fact
or is multiplied by the message class (determined by the Precedence:
field in the user header and the
P
lines in the configuration file) and subtracted from the
priority. Thus, messages with a higher Priority: will be favored. Defaults to 1800.
ClientCertFile File containing the certificate of the client, i.e., this certificate is used when
sendmail
acts
as client (for STARTTLS).
ClientKeyFile File containing the private key belonging to the client certificate (for STARTTLS if
send-
runs as client).
ClientPortOptions=
options
Set client SMTP options. The options are
key=value
pairs separated by commas. Known
keys are:
Port Name/number of source port for connection (defaults to any free port)
Addr Address mask (defaults INADDR_ANY)
Family Address family (defaults to INET)
SndBufSize Size of TCP send buffer
RcvBufSize Size of TCP receive buffer
Modifier Options (flags) for the client
The
Addr
ess mask may be a numeric address in IPv4 dot notation or IPv6 colon notation
or a network name. Note that if a network name is specified, only the first IP address re-
turned for it will be used. This may cause indeterminate behavior for network names that
resolve to multiple addresses. Therefore, use of an address is recommended.
Modifier
can
be the following character:
SMM:08-64 Sendmail Installation and Operation Guide
h
use name of interface for HELO command
A
don’t use AUTH when sending e-mail
S
don’t use STARTTLS when sending e-mail
If ‘‘h’’ is set, the name corresponding to the outgoing interface address (whether chosen via
the Connection parameter or the default) is used for the HELO/EHLO command. How-
ev er, the name must not start with a square bracket and it must contain at least one dot.
This is a simple test whether the name is not an IP address (in square brackets) but a quali-
fied hostname. Note that multiple ClientPortOptions settings are allowed in order to give
settings for each protocol family (e.g., one for Family=inet and one for Family=inet6). A
restriction placed on one family only affects outgoing connections on that particular family.
ClientSSLOptions
A space or comma separated list of SSL related options for the client side. See
SSL_CTX_set_options
(3) for a list; the available values depend on the OpenSSL version
against which
sendmail
is compiled. By default,
SSL_OP_ALL SSL_OP_NO_SSLv2
SSL_OP_NO_TICKET -SSL_OP_TLSEXT_PADDING
are used (if those options are avail-
able). Options can be cleared by preceding them with a minus sign. It is also possible to
specify numerical values, e.g.,
-0x0010
.
ColonOkInAddr If set, colons are acceptable in e-mail addresses (e.g., “host:user”). If not set, colons indi-
cate the beginning of a RFC 822 group construct (“groupname: member1, member2, ...
memberN;”). Doubled colons are always acceptable (“nodename::user”) and proper route-
addr nesting is understood (“<@relay:user@host>”). Furthermore, this option defaults on
if the configuration version level is less than 6 (for back compatibility). However, it must
be off for full compatibility with RFC 822.
ConnectionCacheSize=
N
[k] The maximum number of open connections that will be cached at a time. The default is
one. This delays closing the current connection until either this invocation of
sendmail
needs to connect to another host or it terminates. Setting it to zero defaults to the old be-
havior, that is, connections are closed immediately. Since this consumes file descriptors,
the connection cache should be kept small: 4 is probably a practical maximum.
ConnectionCacheTimeout=
timeout
[K] The maximum amount of time a cached connection will be permitted to idle without
activity. If this time is exceeded, the connection is immediately closed. This value should
be small (on the order of ten minutes). Before
sendmail
uses a cached connection, it al-
ways sends a RSET command to check the connection; if this fails, it reopens the connec-
tion. This keeps your end from failing if the other end times out. The point of this option
is to be a good network neighbor and avoid using up excessive resources on the other end.
The default is five minutes.
ConnectOnlyTo=
address
This can be used to override the connection address (for testing purposes).
ConnectionRateThrottle=
N
If set to a positive value, allow no more than
N
incoming connections in a one second pe-
riod per daemon. This is intended to flatten out peaks and allow the load average checking
to cut in. Defaults to zero (no limits).
ConnectionRateWindowSize=
N
Define the length of the interval for which the number of incoming connections is main-
tained. The default is 60 seconds.
ControlSocketName=
name
Name of the control socket for daemon management. A running
sendmail
daemon can be
controlled through this named socket. Available commands are:
help, mstat, restart, shut-
down,
and
status.
The
status
command returns the current number of daemon children, the
Sendmail Installation and Operation Guide
SMM:08-65
maximum number of daemon children, the free disk space (in blocks) of the queue direc-
tory, and the load average of the machine expressed as an integer. If not set, no control
socket will be available. Solaris and pre-4.4BSD kernel users should see the note in send-
mail/README .
CRLFile=
name
Name of file that contains certificate revocation status, useful for X.509v3 authentication.
Note: if a CRLFile is specified but the file is unusable, STARTTLS is disabled.
CRLPath=
name
Name of directory that contains hashes pointing to certificate revocation status files. Sym-
bolic links can be generated with the following two (Bourne) shell commands:
C=FileName_of_CRL
ln -s $C ‘openssl crl -noout -hash < $C‘.r0
DHParameters This option applies to the server side only. Possible values are:
5
use precomputed 512 bit prime.
1
generate 1024 bit prime
2
generate 2048 bit prime.
i
use included precomputed 2048 bit prime (default).
none do not use Diffie-Hellman.
/path/to/file load prime from file.
This is only required if a cipher suite containing DSA/DH is used. The default is ‘‘i’’
which selects a precomputed, fixed 2048 bit prime. If ‘‘5’’ is selected, then precomputed,
fixed primes are used. Note: this option should not be used (unless necessary for compati-
bility with old implementations). If ‘‘1’’ or ‘‘2’’ is selected, then prime values are com-
puted during startup. Note: this operation can take a significant amount of time on a slow
machine (several seconds), but it is only done once at startup. If ‘‘none’’ is selected, then
TLS cipher suites containing DSA/DH cannot be used. If a file name is specified (which
must be an absolute path), then the primes are read from it. It is recommended to generate
such a file using a command like this:
openssl dhparam -out /etc/mail/dhparams.pem 2048
If the file is not readable or contains unusable data, the default ‘‘i’’ is used instead.
DaemonPortOptions=
options
[O] Set server SMTP options. Each instance of
DaemonPortOptions
leads to an addi-
tional incoming socket. The options are
key=value
pairs. Known keys are:
Name User-definable name for the daemon (defaults to "Daemon#")
Port Name/number of listening port (defaults to "smtp")
Addr Address mask (defaults INADDR_ANY)
Family Address family (defaults to INET)
InputMailFilters List of input mail filters for the daemon
Listen Size of listen queue (defaults to 10)
Modifier Options (flags) for the daemon
SndBufSize Size of TCP send buffer
RcvBufSize Size of TCP receive buffer
children maximum number of children per daemon, see
MaxDaemonChildren
.
DeliveryMode Delivery mode per daemon, see
DeliveryMode
.
refuseLA RefuseLA per daemon
delayLA DelayLA per daemon
queueLA QueueLA per daemon
The
Name
key is used for error messages and logging. The
Addr
ess mask may be a nu-
meric address in IPv4 dot notation or IPv6 colon notation, or a network name, or a path to
a local socket. Note that if a network name is specified, only the first IP address returned
for it will be used. This may cause indeterminate behavior for network names that resolve
SMM:08-66 Sendmail Installation and Operation Guide
to multiple addresses. Therefore, use of an address is recommended. The
Family
key de-
faults to INET (IPv4). IPv6 users who wish to also accept IPv6 connections should add
additional Family=inet6
DaemonPortOptions
lines. For a local socket, use Family=local
or Family=unix. The
InputMailFilters
key overrides the default list of input mail filters
listed in the
InputMailFilters
option. If multiple input mail filters are required, they must
be separated by semicolons (not commas).
Modifier
can be a sequence (without any de-
limiters) of the following characters:
a
always require AUTH
b
bind to interface through which mail has been received
c
perform hostname canonification (.cf)
f
require fully qualified hostname (.cf)
s
Run smtps (SMTP over SSL) instead of smtp
u
allow unqualified addresses (.cf)
A
disable AUTH (overrides ’a’ modifier)
C
don’t perform hostname canonification
E
disallow ETRN (see RFC 2476)
O
optional; if opening the socket fails ignore it
S
don’t offer STARTTLS
That is, one way to specify a message submission agent (MSA) that always requires AUTH
is:
O DaemonPortOptions=Name=MSA, Port=587, M=Ea
The modifiers that are marked with "(.cf)" have only effect in the standard configuration
file, in which they are available via
${daemon_flags}
. Notice: Do
not
use the ‘‘a’’ modi-
fier on a public accessible MTA! It should only be used for a MSA that is accessed by au-
thorized users for initial mail submission. Users must authenticate to use a MSA which
has this option turned on. The flags ‘‘c’’ and ‘‘C’’ can change the default for hostname
canonification in the
sendmail.cf
file. See the relevant documentation for
FEATURE(no-
canonify)
. The modifier ‘‘f ’’ disallows addresses of the form
user@host
unless they are
submitted directly. The flag ‘‘u’’ allows unqualified sender addresses, i.e., those without
@host. ‘‘b’’ forces sendmail to bind to the interface through which the e-mail has been re-
ceived for the outgoing connection.
WARNING:
Use ‘‘b’’ only if outgoing mail can be
routed through the incoming connection’s interface to its destination. No attempt is made
to catch problems due to a misconfiguration of this parameter, use it only for virtual host-
ing where each virtual interface can connect to every possible location. This will also
override possible settings via
ClientPortOptions.
Note,
sendmail
will listen on a new
socket for each occurrence of the
DaemonPortOptions
option in a configuration file. The
modifier ‘‘O’’ causes sendmail to ignore a socket if it can’t be opened. This applies to fail-
ures from the socket(2) and bind(2) calls.
DefaultAuthInfo Filename that contains default authentication information for outgoing connections. This
file must contain the user id, the authorization id, the password (plain text), the realm and
the list of mechanisms to use on separate lines and must be readable by root (or the trusted
user) only. If no realm is specified,
$j
is used. If no mechanisms are specified, the list
given by
AuthMechanisms
is used. Notice: this option is deprecated and will be removed
in future versions. Moreover, it doesn’t work for the MSP since it can’t read the file (the
file must not be group/world-readable otherwise
sendmail
will complain). Use the au-
thinfo ruleset instead which provides more control over the usage of the data anyway.
DefaultCharSet=
charset
When a message that has 8-bit characters but is not in MIME format is converted to MIME
(see the EightBitMode option) a character set must be included in the Content-Type:
header. This character set is normally set from the Charset= field of the mailer descriptor.
If that is not set, the value of this option is used. If this option is not set, the value
Sendmail Installation and Operation Guide
SMM:08-67
“unknown-8bit” is used.
DataFileBufferSize=
threshold
Set the
threshold
, in bytes, before a memory-based queue data file becomes disk-based.
The default is 4096 bytes.
DeadLetterDrop=
file
Defines the location of the system-wide dead.letter file, formerly hardcoded to
/usr/tmp/dead.letter. If this option is not set (the default), sendmail will not attempt to save
to a system-wide dead.letter file in the event it cannot bounce the mail to the user or post-
master. Instead, it will rename the qf file as it has in the past when the dead.letter file could
not be opened.
DefaultUser=
user:group
[u] Set the default userid for mailers to
user:group
. If
group
is omitted and
user
is a user
name (as opposed to a numeric user id) the default group listed in the /etc/passwd file for
that user is used as the default group. Both
user
and
group
may be numeric. Mailers with-
out the
S
flag in the mailer definition will run as this user. Defaults to 1:1. The value can
also be given as a symbolic user name.
19
DelayLA=
LA
When the system load average exceeds
LA
,
sendmail
will sleep for one second on most
SMTP commands and before accepting connections.
DeliverByMin=
time
Set minimum time for Deliver By SMTP Service Extension (RFC 2852). If 0, no time is
listed, if less than 0, the extension is not offered, if greater than 0, it is listed as minimum
time for the EHLO keyword DELIVERBY.
DeliveryMode=
x
[d] Deliver in mode
x
. Leg al modes are:
i
Deliver interactively (synchronously)
b
Deliver in background (asynchronously)
q
Just queue the message (deliver during queue run)
d
Defer delivery and all map lookups (deliver during queue run)
Defaults to ‘‘b’’ if no option is specified, ‘‘i’’ if it is specified but given no argument (i.e.,
‘‘Od’’ is equivalent to ‘‘Odi’’). The
−v
command line flag sets this to
i
. Note: for internal
reasons, ‘‘i’’ does not work if a milter is enabled which can reject or delete recipients. In
that case the mode will be changed to ‘‘b’’.
DialDelay=
sleeptime
Dial-on-demand network connections can see timeouts if a connection is opened before the
call is set up. If this is set to an interval and a connection times out on the first connection
being attempted
sendmail
will sleep for this amount of time and try again. This should
give your system time to establish the connection to your service provider. Units default to
seconds, so “DialDelay=5” uses a five second delay. Defaults to zero (no retry). This de-
lay only applies to mailers which have the Z flag set.
DirectSubmissionModifiers=
modifiers
Defines
${daemon_flags}
for direct (command line) submissions. If not set,
${dae-
mon_flags}
is either "CC f" if the option
−G
is used or "c u" otherwise. Note that only the
"CC", "c", "f", and "u" flags are checked.
DontBlameSendmail=
option,option,...
In order to avoid possible cracking attempts caused by world- and group-writable files and
directories,
sendmail
does paranoid checking when opening most of its support files. If for
19
The old
g
option has been combined into the
DefaultUser
option.
SMM:08-68 Sendmail Installation and Operation Guide
some reason you absolutely must run with, for example, a group-writable
/etc
directory,
then you will have to turn off this checking (at the cost of making your system more vul-
nerable to attack). The possible arguments have been described earlier. The details of
these flags are described above.
Use of this option is not recommended.
DontExpandCnames
The standards say that all host addresses used in a mail message must be fully canonical.
For example, if your host is named “Cruft.Foo.ORG” and also has an alias of
“FTP.Foo.ORG”, the former name must be used at all times. This is enforced during host
name canonification ($[ ... $] lookups). If this option is set, the protocols are ignored and
the “wrong” thing is done. However, the IETF is moving toward changing this standard, so
the behavior may become acceptable. Please note that hosts downstream may still rewrite
the address to be the true canonical name however.
DontInitGroups If set,
sendmail
will avoid using the initgroups(3) call. If you are running NIS, this causes
a sequential scan of the groups.byname map, which can cause your NIS server to be badly
overloaded in a large domain. The cost of this is that the only group found for users will
be their primary group (the one in the password file), which will make file access permis-
sions somewhat more restrictive. Has no effect on systems that don’t hav e group lists.
DontProbeInterfaces
Sendmail
normally finds the names of all interfaces active on your machine when it starts
up and adds their name to the
$=w
class of known host aliases. If you have a large number
of virtual interfaces or if your DNS inverse lookups are slow this can be time consuming.
This option turns off that probing. However, you will need to be certain to include all vari-
ant names in the
$=w
class by some other mechanism. If set to
loopback
, loopback inter-
faces (e.g., lo0) will not be probed.
DontPruneRoutes [R] Normally,
sendmail
tries to eliminate any unnecessary explicit routes when sending an
error message (as discussed in RFC 1123 § 5.2.6). For example, when sending an error
message to
<@known1,@known2,@known3:user@unknown>
sendmail
will strip off the “@known1,@known2” in order to make the route as direct as
possible. However, if the
R
option is set, this will be disabled, and the mail will be sent to
the first address in the route, even if later addresses are known. This may be useful if you
are caught behind a firewall.
DoubleBounceAddress=
error-address
If an error occurs when sending an error message, send the error report (termed a “double
bounce” because it is an error “bounce” that occurs when trying to send another error
“bounce”) to the indicated address. The address is macro expanded at the time of delivery.
If not set, defaults to “postmaster”. If set to an empty string, double bounces are dropped.
EightBitMode=
action
[8] Set handling of eight-bit data. There are two kinds of eight-bit data: that declared as
such using the
BODY=8BITMIME
ESMTP declaration or the
−B8BITMIME
command
line flag, and undeclared 8-bit data, that is, input that just happens to be eight bits. There
are three basic operations that can happen: undeclared 8-bit data can be automatically con-
verted to 8BITMIME, undeclared 8-bit data can be passed as-is without conversion to
MIME (‘‘just send 8’’), and declared 8-bit data can be converted to 7-bits for transmission
to a non-8BITMIME mailer. The possible
action
s are:
s
Reject undeclared 8-bit data (‘‘strict’’)
m Convert undeclared 8-bit data to MIME (‘‘mime’’)
p
Pass undeclared 8-bit data (‘‘pass’’)
In all cases properly declared 8BITMIME data will be converted to 7BIT as needed. Note:
Sendmail Installation and Operation Guide
SMM:08-69
if an automatic conversion is performed, a header with the following format will be added:
X-MIME-Autoconverted: from OLD to NEW by $j id $i
where OLD and NEW describe the original format and the converted format, respectively.
ErrorHeader=
file-or-message
[E] Prepend error messages with the indicated message. If it begins with a slash, it is as-
sumed to be the pathname of a file containing a message (this is the recommended setting).
Otherwise, it is a literal message. The error file might contain the name, email address,
and/or phone number of a local postmaster who could provide assistance to end users. If
the option is missing or null, or if it names a file which does not exist or which is not read-
able, no message is printed.
ErrorMode=
x
[e] Dispose of errors using mode
x
. The values for
x
are:
p
Print error messages (default)
q
No messages, just give exit status
m
Mail back errors
w
Write back errors (mail if user not logged in)
e
Mail back errors (when applicable) and give zero exit stat always
Note that the last mode, “e”, is for Berknet error processing and should not be used in nor-
mal circumstances. Note, too, that mode “q”, only applies to errors recognized before
sendmail forks for background delivery.
FallbackMXhost=
fallbackhost
[V] If specified, the
fallbackhost
acts like a very low priority MX on a host. MX records
will be looked up for this host, unless the name is surrounded by square brackets. This is
intended to be used by sites with poor network connectivity. Messages which are undeliv-
erable due to temporary address failures (e.g., DNS failure) also go to the FallbackMXhost.
FallBackSmartHost=
hostname
If specified, the
FallBackSmartHost
will be used in a last-ditch effort for a host. This is in-
tended to be used by sites with "fake internal DNS", e.g., a company whose DNS accu-
rately reflects the world inside that company’s domain but not outside.
FastSplit If set to a value greater than zero (the default is one), it suppresses the MX lookups on ad-
dresses when they are initially sorted, i.e., for the first delivery attempt. This usually re-
sults in faster envelope splitting unless the MX records are readily available in a local DNS
cache. To enforce initial sorting based on MX records set
FastSplit
to zero. If the mail is
submitted directly from the command line, then the value also limits the number of
processes to deliver the envelopes; if more envelopes are created they are only queued up
and must be taken care of by a queue run. Since the default submission method is via
SMTP (either from a MUA or via the MSP), the value of
FastSplit
is seldom used to limit
the number of processes to deliver the envelopes.
ForkEachJob [Y] If set, deliver each job that is run from the queue in a separate process.
ForwardPath=
path
[J] Set the path for searching for users’ .forward files. The default is “$z/.forward”. Some
sites that use the automounter may prefer to change this to “/var/forward/$u” to search a
file with the same name as the user in a system directory. It can also be set to a sequence
of paths separated by colons;
sendmail
stops at the first file it can successfully and safely
open. For example, “/var/forward/$u:$z/.forward” will search first in /var/forward/
user-
name
and then in
˜username
/.forward (but only if the first file does not exist).
HeloName=
name
Set the name to be used for HELO/EHLO (instead of $j).
HelpFile=
file
[H] Specify the help file for SMTP. If no file name is specified, "helpfile" is used. If the
help file does not exist (cannot be opened for reading)
sendmail
will print a note including
SMM:08-70 Sendmail Installation and Operation Guide
its version in response to a
HELP
command. To avoid providing this information to a
client specify an empty file.
HoldExpensive [c] If an outgoing mailer is marked as being expensive, don’t connect immediately.
HostsFile=
path
The path to the hosts database, normally “/etc/hosts”. This option is only consulted when
sendmail is canonifying addresses, and then only when “files” is in the “hosts” service
switch entry. In particular, this file is
never
used when looking up host addresses; that is
under the control of the system
gethostbyname
(3) routine.
HostStatusDirectory=
path
The location of the long term host status information. When set, information about the sta-
tus of hosts (e.g., host down or not accepting connections) will be shared between all
send-
processes; normally, this information is only held within a single queue run. This op-
tion requires a connection cache of at least 1 to function. If the option begins with a lead-
ing ‘/’, it is an absolute pathname; otherwise, it is relative to the mail queue directory. A
suggested value for sites desiring persistent host status is “.hoststat” (i.e., a subdirectory of
the queue directory).
IgnoreDots [i] Do not treat leading dots in incoming messages in a special way, e.g., as end of a mes-
sage if it is the only character in a line. This is always disabled when reading SMTP mail.
InputMailFilters=
name,name,...
A comma separated list of filters which determines which filters (see the "X — Mail Filter
(Milter) Definitions" section) and the invocation sequence are contacted for incoming
SMTP messages. If none are set, no filters will be contacted.
LDAPDefaultSpec=
spec
Sets a default map specification for LDAP maps. The value should only contain LDAP
specific settings such as “-h host -p port -d bindDN”. The settings will be used for all
LDAP maps unless the individual map specification overrides a setting. This option should
be set before any LDAP maps are defined.
LogLevel=
n
[L] Set the log level to
n
. Defaults to 9.
M
x value
[no long version] Set the macro
x
to
value
. This is intended only for use from the com-
mand line. The
−M
flag is preferred.
MailboxDatabase Type of lookup to find information about local mailboxes, defaults to ‘‘pw’’ which uses
getpwnam
(3). Other types can be introduced by adding them to the source code, see
libsm/mbdb.c for details.
UseMSP Use as mail submission program, i.e., allow group writable queue files if the group is the
same as that of a set-group-ID sendmail binary. See the file
sendmail/SECURITY
in the
distribution tarball.
MatchGECOS [G] Allow fuzzy matching on the GECOS field. If this flag is set, and the usual user name
lookups fail (that is, there is no alias with this name and a
getpwnam
(3) fails), sequentially
search the password file for a matching entry in the GECOS field. This also requires that
MATCHGECOS be turned on during compilation. This option is not recommended.
MaxAliasRecursion=
N
The maximum depth of alias recursion (default: 10).
MaxDaemonChildren=
N
If set,
sendmail
will refuse connections when it has more than
N
children processing in-
coming mail or automatic queue runs. This does not limit the number of outgoing connec-
tions. If the default
DeliveryMode
(background) is used, then
sendmail
may create an al-
most unlimited number of children (depending on the number of transactions and the rela-
tive execution times of mail reception and mail delivery). If the limit should be enforced,
then a
DeliveryMode
other than background must be used. If not set, there is no limit to
Sendmail Installation and Operation Guide
SMM:08-71
the number of children -- that is, the system load average controls this.
MaxHeadersLength=
N
If set to a value greater than zero it specifies the maximum length of the sum of all headers.
This can be used to prevent a denial of service attack. The default is 32K.
MaxHopCount=
N
[h] The maximum hop count. Messages that have been processed more than
N
times are
assumed to be in a loop and are rejected. Defaults to 25.
MaxMessageSize=
N
Specify the maximum message size to be advertised in the ESMTP EHLO response. Mes-
sages larger than this will be rejected. If set to a value greater than zero, that value will be
listed in the SIZE response, otherwise SIZE is advertised in the ESMTP EHLO response
without a parameter.
MaxMimeHeaderLength=
N[/M]
Sets the maximum length of certain MIME header field values to
N
characters. These
MIME header fields are determined by being a member of class {checkMIMETextHead-
ers}, which currently contains only the header Content-Description. For some of these
headers which take parameters, the maximum length of each parameter is set to
M
if speci-
fied. If
/M
is not specified, one half of
N
will be used. By default, these values are 2048
and 1024, respectively. To allow any length, a value of 0 can be specified.
MaxNOOPCommands=
N
Override the default of
MAXNOOPCOMMANDS
for the number of
useless
commands,
see Section "Measures against Denial of Service Attacks".
MaxQueueChildren=
N
When set, this limits the number of concurrent queue runner processes to
N.
This helps to
control the amount of system resources used when processing the queue. When there are
multiple queue groups defined and the total number of queue runners for these queue
groups would exceed
MaxQueueChildren
then the queue groups will not all run concur-
rently. That is, some portion of the queue groups will run concurrently such that
Max-
QueueChildren
will not be exceeded, while the remaining queue groups will be run later
(in round robin order). See also
MaxRunnersPerQueue
and the section
Queue Group Dec-
laration
. Notice:
sendmail
does not count individual queue runners, but only sets of
processes that act on a workgroup. Hence the actual number of queue runners may be
lower than the limit imposed by
MaxQueueChildren
. This discrepancy can be large if
some queue runners have to wait for a slow server and if short intervals are used.
MaxQueueRunSize=
N
The maximum number of jobs that will be processed in a single queue run. If not set, there
is no limit on the size. If you have very large queues or a very short queue run interval this
could be unstable. However, since the first
N
jobs in queue directory order are run (rather
than the
N
highest priority jobs) this should be set as high as possible to avoid “losing”
jobs that happen to fall late in the queue directory. Note: this option also restricts the num-
ber of entries printed by
mailq
. That is, if
MaxQueueRunSize
is set to a value
N
larger
than zero, then only
N
entries are printed per queue group.
MaxRecipientsPerMessage=
N
The maximum number of recipients that will be accepted per message in an SMTP transac-
tion. Note: setting this too low can interfere with sending mail from MUAs that use SMTP
for initial submission. If not set, there is no limit on the number of recipients per envelope.
MaxRunnersPerQueue=
N
This sets the default maximum number of queue runners for queue groups. Up to
N
queue
runners will work in parallel on a queue group’s messages. This is useful where the pro-
cessing of a message in the queue might delay the processing of subsequent messages.
SMM:08-72 Sendmail Installation and Operation Guide
Such a delay may be the result of non-erroneous situations such as a low bandwidth con-
nection. May be overridden on a per queue group basis by setting the
Runners
option; see
the section
Queue Group Declaration
. The default is 1 when not set.
MeToo [m] Send to me too, even if I am in an alias expansion. This option is deprecated and will
be removed from a future version.
Milter This option has several sub(sub)options. The names of the suboptions are separated by
dots. At the first level the following options are available:
LogLevel
Log level for input mail filter actions, defaults to LogLevel.
macros Specifies list of macro to transmit to filters.
See list below.
The ‘‘macros’’ option has the following suboptions which specify the list of macro to trans-
mit to milters after a certain event occurred.
connect After session connection start
helo After EHLO/HELO command
envfrom After MAIL command
envrcpt After RCPT command
data After DATA command.
eoh After DATA command and header
eom After DATA command and terminating ‘‘.’’
By default the lists of macros are empty. Example:
O Milter.LogLevel=12
O Milter.macros.connect=j, _, {daemon_name}
MinFreeBlocks=
N
[b] Insist on at least
N
blocks free on the filesystem that holds the queue files before ac-
cepting email via SMTP. If there is insufficient space
sendmail
gives a 452 response to the
MAIL command. This invites the sender to try again later.
MaxQueueAge=
age
If this is set to a value greater than zero, entries in the queue will be retried during a queue
run only if the individual retry time has been reached. The time for the next retry depends
on the time passed since the job was last processed. The maximum retry time is limited by
the specified value.
MinQueueAge=
age
Don’t process any queued jobs that have been in the queue less than the indicated time in-
terval. This is intended to allow you to get responsiveness by processing the queue fairly
frequently without thrashing your system by trying jobs too often. The default units are
minutes. Note: This option is ignored for queue runs that select a subset of the queue, i.e.,
“−q[!][I|R|S|Q][string]”
MustQuoteChars=
s
Sets the list of characters that must be quoted if used in a full name that is in the phrase
part of a ‘‘phrase <address>’’ syntax. The default is ‘‘´.’’. The characters ‘‘@,;:\()[]’’ are
always added to this list. Note: To avoid potential breakage of DKIM signatures it is use-
ful to set
O MustQuoteChars=.
Moreover, relaxed header signing should be used for DKIM signatures.
NiceQueueRun The priority of queue runners (nice(3)). This value must be greater or equal zero.
NoRecipientAction
The action to take when you receive a message that has no valid recipient headers (To:,
Sendmail Installation and Operation Guide
SMM:08-73
Cc:, Bcc:, or Apparently-To: — the last included for back compatibility with old
send-
s). It can be
None
to pass the message on unmodified, which violates the protocol,
Add-To
to add a To: header with any recipients it can find in the envelope (which might
expose Bcc: recipients),
Add-Apparently-To
to add an Apparently-To: header (this is only
for back-compatibility and is officially deprecated),
Add-To-Undisclosed
to add a header
“To: undisclosed-recipients:;” to make the header legal without disclosing anything, or
Add-Bcc
to add an empty Bcc: header.
OldStyleHeaders [o] Assume that the headers may be in old format, i.e., spaces delimit names. This actually
turns on an adaptive algorithm: if any recipient address contains a comma, parenthesis, or
angle bracket, it will be assumed that commas already exist. If this flag is not on, only
commas delimit names. Headers are always output with commas between the names. De-
faults to off.
OperatorChars=
charlist
[$o macro] The list of characters that are considered to be “operators”, that is, characters
that delimit tokens. All operator characters are tokens by themselves; sequences of non-
operator characters are also tokens. White space characters separate tokens but are not to-
kens themselves — for example, “AAA.BBB” has three tokens, but “AAA BBB” has two.
If not set, OperatorChars defaults to “. : @ [ ]”; additionally, the characters “( ) < > , ;” are
always operators. Note that OperatorChars must be set in the configuration file before any
rulesets.
PidFile=
filename
Filename of the pid file. (default is _PATH_SENDMAILPID). The
filename
is macro-ex-
panded before it is opened, and unlinked when
sendmail
exits.
PostmasterCopy=
postmaster
[P] If set, copies of error messages will be sent to the named
postmaster
. Only the header
of the failed message is sent. Errors resulting from messages with a negative precedence
will not be sent. Since most errors are user problems, this is probably not a good idea on
large sites, and arguably contains all sorts of privacy violations, but it seems to be popular
with certain operating systems vendors. The address is macro expanded at the time of de-
livery. Defaults to no postmaster copies.
PrivacyOptions=
opt,opt,...
[p] Set the privacy
opt
ions. ‘‘Privacy’’ is really a misnomer; many of these are just a way
of insisting on stricter adherence to the SMTP protocol. The
opt
ions can be selected from:
public Allow open access
needmailhelo Insist on HELO or EHLO command before MAIL
needexpnhelo Insist on HELO or EHLO command before EXPN
noexpn Disallow EXPN entirely, implies noverb.
needvrfyhelo Insist on HELO or EHLO command before VRFY
novrfy Disallow VRFY entirely
noetrn Disallow ETRN entirely
noverb Disallow VERB entirely
restrictmailq Restrict mailq command
restrictqrun Restrict −q command line flag
restrictexpand Restrict −bv and −v command line flags
noreceipts Don’t return success DSNs
20
nobodyreturn Don’t return the body of a message with DSNs
goaway
Disallow essentially all SMTP status queries
authwarnings Put X-Authentication-Warning: headers in messages
and log warnings
noactualrecipient Don’t put X-Actual-Recipient lines in DSNs
which reveal the actual account that addresses map to.
SMM:08-74 Sendmail Installation and Operation Guide
The “goaway” pseudo-flag sets all flags except “noreceipts”, “restrictmailq”, “restric-
tqrun”, “restrictexpand”, “noetrn”, and “nobodyreturn”. If mailq is restricted, only people
in the same group as the queue directory can print the queue. If queue runs are restricted,
only root and the owner of the queue directory can run the queue. The “restrictexpand”
pseudo-flag instructs
sendmail
to drop privileges when the
−bv
option is given by users
who are neither root nor the TrustedUser so users cannot read private aliases, forwards, or
:include: files. It will add the “NonRootSafeAddr” to the “DontBlameSendmail” option to
prevent misleading unsafe address warnings. It also overrides the
−v
(verbose) command
line option to prevent information leakage. Authentication Warnings add warnings about
various conditions that may indicate attempts to spoof the mail system, such as using a
non-standard queue directory.
ProcessTitlePrefix=
string
Prefix the process title shown on ’ps’ listings with
string
. The
string
will be macro
processed.
QueueDirectory=
dir
[Q] The QueueDirectory option serves two purposes. First, it specifies the directory or set
of directories that comprise the default queue group. Second, it specifies the directory D
which is the ancestor of all queue directories, and which sendmail uses as its current work-
ing directory. When sendmail dumps core, it leaves its core files in D. There are two
cases. If
dir
ends with an asterisk (eg,
/var/spool/mqueue/qd*
), then all of the directories
or symbolic links to directories beginning with ‘qd’ in
/var/spool/mqueue
will be used as
queue directories of the default queue group, and
/var/spool/mqueue
will be used as the
working directory D. Otherwise,
dir
must name a directory (usually
/var/spool/mqueue
):
the default queue group consists of the single queue directory
dir
, and the working direc-
tory D is set to
dir
. To define additional groups of queue directories, use the configuration
file ‘Q’ command. Do not change the queue directory structure while sendmail is running.
QueueFactor=
factor
[q] Use
factor
as the multiplier in the map function to decide when to just queue up jobs
rather than run them. This value is divided by the difference between the current load aver-
age and the load average limit (
QueueLA
option) to determine the maximum message pri-
ority that will be sent. Defaults to 600000.
QueueLA=
LA
[x] When the system load average exceeds
LA
and the
QueueFactor
(
q
) option divided by
the difference in the current load average and the
QueueLA
option plus one is less than the
priority of the message, just queue messages (i.e., don’t try to send them). Defaults to 8
multiplied by the number of processors online on the system (if that can be determined).
QueueFileMode=
mode
Default permissions for queue files (octal). If not set, sendmail uses 0600 unless its real
and effective uid are different in which case it uses 0644.
QueueSortOrder=
algorithm
Sets the
algorithm
used for sorting the queue. Only the first character of the value is used.
Legal values are “host” (to order by the name of the first host name of the first recipient),
“filename” (to order by the name of the queue file name), “time” (to order by the submis-
sion/creation time), “random” (to order randomly), “modification” (to order by the modifi-
cation time of the qf file (older entries first)), “none” (to not order), and “priority” (to order
by message priority). Host ordering makes better use of the connection cache, but may
tend to process low priority messages that go to a single host over high priority messages
that go to several hosts; it probably shouldn’t be used on slow network links. Filename and
20
N.B.: the
noreceipts
flag turns off support for RFC 1891 (Delivery Status Notification).
Sendmail Installation and Operation Guide
SMM:08-75
modification time ordering saves the overhead of reading all of the queued items before
starting the queue run. Creation (submission) time ordering is almost always a bad idea,
since it allows large, bulk mail to go out before smaller, personal mail, but may have ap-
plicability on some hosts with very fast connections. Random is useful if several queue
runners are started by hand which try to drain the same queue since odds are they will be
working on different parts of the queue at the same time. Priority ordering is the default.
QueueTimeout=
timeout
[T] A synonym for “Timeout.queuereturn”. Use that form instead of the “QueueTimeout”
form.
RandFile Name of file containing random data or the name of the UNIX socket if EGD is used. A
(required) prefix "egd:" or "file:" specifies the type. STARTTLS requires this filename if
the compile flag HASURANDOMDEV is not set (see sendmail/README).
ResolverOptions=
options
[I] Set resolver options. Values can be set using
+
flag
and cleared using
−
flag
; the
flag
s
can be “debug”, “aaonly”, “usevc”, “primary”, “igntc”, “recurse”, “defnames”, “stayopen”,
“use_inet6”, or “dnsrch”. The string “HasWildcardMX” (without a
+
or
−
) can be speci-
fied to turn off matching against MX records when doing name canonifications. The string
“WorkAroundBrokenAAAA” (without a
+
or
−
) can be specified to work around some
broken nameservers which return SERVFAIL (a temporary failure) on T_AAAA (IPv6)
lookups. Notice: it might be necessary to apply the same (or similar) options to
submit.cf
too.
RequiresDirfsync This option can be used to override the compile time flag
REQUIRES_DIR_FSYNC
at
runtime by setting it to
false
. If the compile time flag is not set, the option is ignored. The
flag turns on support for file systems that require to call
fsync()
for a directory if the meta-
data in it has been changed. This should be turned on at least for older versions of Reis-
erFS; it is enabled by default for Linux. According to some information this flag is not
needed anymore for kernel 2.4.16 and newer.
RrtImpliesDsn If this option is set, a “Return-Receipt-To:” header causes the request of a DSN, which is
sent to the envelope sender as required by RFC 1891, not to the address given in the
header.
RunAsUser=
user
The
user
parameter may be a user name (looked up in
/etc/passwd
) or a numeric user id;
either form can have “:group” attached (where group can be numeric or symbolic). If set
to a non-zero (non-root) value,
sendmail
will change to this user id shortly after startup
21
.
This avoids a certain class of security problems. However, this means that all “.forward”
and “:include:” files must be readable by the indicated
user
and all files to be written must
be writable by
user
Also, all file and program deliveries will be marked unsafe unless the
option
DontBlameSendmail=NonRootSafeAddr
is set, in which case the delivery will be
done as
user
. It is also incompatible with the
SafeFileEnvironment
option. In other
words, it may not actually add much to security on an average system, and may in fact de-
tract from security (because other file permissions must be loosened). However, it should
be useful on firewalls and other places where users don’t hav e accounts and the aliases file
is well constrained.
RecipientFactor=
fact
[y] The indicated
fact
or is added to the priority (thus
lowering
the priority of the job) for
each recipient, i.e., this value penalizes jobs with large numbers of recipients. Defaults to
30000.
21
When running as a daemon, it changes to this user after accepting a connection but before reading any
SMTP
commands.
SMM:08-76 Sendmail Installation and Operation Guide
RefuseLA=
LA
[X] When the system load average exceeds
LA
, refuse incoming SMTP connections. De-
faults to 12 multiplied by the number of processors online on the system (if that can be de-
termined).
RejectLogInterval=
timeout
Log interval when refusing connections for this long (default: 3h).
RetryFactor=
fact
[Z] The
fact
or is added to the priority every time a job is processed. Thus, each time a job
is processed, its priority will be decreased by the indicated value. In most environments
this should be positive, since hosts that are down are all too often down for a long time.
Defaults to 90000.
SafeFileEnvironment=
dir
If this option is set,
sendmail
will do a
chroot
(2) call into the indicated
dir
ectory before
doing any file writes. If the file name specified by the user begins with
dir
, that partial
path name will be stripped off before writing, so (for example) if the SafeFileEnvironment
variable is set to “/safe” then aliases of “/safe/logs/file” and “/logs/file” actually indicate
the same file. Additionally, if this option is set,
sendmail
refuses to deliver to symbolic
links.
SaveFromLine [f] Save UNIX-style “From” lines at the front of headers. Normally they are assumed re-
dundant and discarded.
SendMimeErrors [j] If set, send error messages in MIME format (see RFC 2045 and RFC 1344 for details).
If disabled,
sendmail
will not return the DSN keyword in response to an EHLO and will
not do Delivery Status Notification processing as described in RFC 1891.
ServerCertFile File containing the certificate of the server, i.e., this certificate is used when sendmail acts
as server (used for STARTTLS).
ServerKeyFile File containing the private key belonging to the server certificate (used for STARTTLS).
ServerSSLOptions
A space or comma separated list of SSL related options for the server side. See
SSL_CTX_set_options
(3) for a list; the available values depend on the OpenSSL version
against which
sendmail
is compiled.
By default,
SSL_OP_ALL -SSL_OP_TL-
SEXT_PADDING
are used (if those options are available). Options can be cleared by pre-
ceding them with a minus sign. It is also possible to specify numerical values, e.g.,
-0x0010
.
ServiceSwitchFile=
filename
If your host operating system has a service switch abstraction (e.g., /etc/nsswitch.conf on
Solaris or /etc/svc.conf on Ultrix and DEC OSF/1) that service will be consulted and this
option is ignored. Otherwise, this is the name of a file that provides the list of methods
used to implement particular services. The syntax is a series of lines, each of which is a
sequence of words. The first word is the service name, and following words are service
types. The services that
sendmail
consults directly are “aliases” and “hosts.” Service
types can be “dns”, “nis”, “nisplus”, or “files” (with the caveat that the appropriate support
must be compiled in before the service can be referenced). If ServiceSwitchFile is not
specified, it defaults to /etc/mail/service.switch. If that file does not exist, the default
switch is:
aliases files
hosts dns nis files
The default file is “/etc/mail/service.switch”.
SevenBitInput [7] Strip input to seven bits for compatibility with old systems. This shouldn’t be neces-
sary.
Sendmail Installation and Operation Guide
SMM:08-77
SharedMemoryKey
Ke y to use for shared memory segment; if not set (or 0), shared memory will not be used.
If set to -1
sendmail
can select a key itself provided that also
SharedMemoryKeyFile
is
set. Requires support for shared memory to be compiled into
sendmail
. If this option is
set,
sendmail
can share some data between different instances. For example, the number
of entries in a queue directory or the available space in a file system. This allows for more
efficient program execution, since only one process needs to update the data instead of
each individual process gathering the data each time it is required.
SharedMemoryKeyFile
If
SharedMemoryKey
is set to -1 then the automatically selected shared memory key will
be stored in the specified file.
SingleLineFromHeader
If set, From: lines that have embedded newlines are unwrapped onto one line. This is to
get around a botch in Lotus Notes that apparently cannot understand legally wrapped RFC
822 headers.
SingleThreadDelivery
If set, a client machine will never try to open two SMTP connections to a single server ma-
chine at the same time, even in different processes. That is, if another
sendmail
is already
talking to some host a new
sendmail
will not open another connection. This property is of
mixed value; although this reduces the load on the other machine, it can cause mail to be
delayed (for example, if one
sendmail
is delivering a huge message, other
sendmail
s won’t
be able to send even small messages). Also, it requires another file descriptor (for the lock
file) per connection, so you may have to reduce the
ConnectionCacheSize
option to avoid
running out of per-process file descriptors. Requires the
HostStatusDirectory
option.
SmtpGreetingMessage=
message
[$e macro] The message printed when the SMTP server starts up. Defaults to “$j Sendmail
$v ready at $b”.
SMTPUTF8 Enable runtime support for SMTPUTF8.
SoftBounce If set, issue temporary errors (4xy) instead of permanent errors (5xy). This can be useful
during testing of a new configuration to avoid erroneous bouncing of mails.
SSLEngine Name of SSL engine to use. The available values depend on the OpenSSL version against
which
sendmail
is compiled, see
openssl engine -v
for some information.
SSLEnginePath Path to dynamic library for SSL engine. This option is only useful if
SSLEngine
is set. If
both are set, the engine will be loaded dynamically at runtime using the concatenation of
the path, a slash "/", the string "lib", the value of
SSLEngine
, and the string ".so". If only
SSLEngine
is set then the static version of the engine is used.
StatusFile=
file
[S] Log summary statistics in the named
file
. If no file name is specified, "statistics" is
used. If not set, no summary statistics are saved. This file does not grow in size. It can be
printed using the
mailstats
(8) program.
SuperSafe [s] This option can be set to True, False, Interactive, or PostMilter. If set to True,
sendmail
will be super-safe when running things, i.e., always instantiate the queue file, even if you
are going to attempt immediate delivery.
Sendmail
always instantiates the queue file be-
fore returning control to the client under any circumstances. This should really
always
be
set to True. The Interactive value has been introduced in 8.12 and can be used together
with
DeliveryMode=i
. It skips some synchronization calls which are effectively doubled
in the code execution path for this mode. If set to PostMilter,
sendmail
defers synchroniz-
ing the queue file until any milters have signaled acceptance of the message. PostMilter is
SMM:08-78 Sendmail Installation and Operation Guide
useful only when
sendmail
is running as an SMTP server; in all other situations it acts the
same as True.
TLSFallbacktoClear
If set,
sendmail
immediately tries an outbound connection again without STARTTLS after
a TLS handshake failure. Note: this applies to all connections even if TLS specific require-
ments are set (see rulesets
tls_rcpt
and
tls_client
). Hence such requirements will cause an
error on a retry without STARTTLS. Therefore they should only trigger a temporary fail-
ure so the connection is later on tried again.
TLSSrvOptions List of options for SMTP STARTTLS for the server consisting of single characters with in-
tervening white space or commas. The flag ‘‘V’’ disables client verification, and hence it is
not possible to use a client certificate for relaying. The flag ‘‘C’’ removes the requirement
for the TLS server to have a cert. This only works under very specific circumstances and
should only be used if the consequences are understood, e.g., clients may not work with a
server using this.
TempFileMode=
mode
[F] The file mode for transcript files, files to which
sendmail
delivers directly, files in the
HostStatusDirectory
, and
StatusFile
. It is interpreted in octal by default. Defaults to
0600.
Timeout.
type
=
timeout
[r; subsumes old T option as well] Set timeout values. For more information, see section
4.1.
TimeZoneSpec=
tzinfo
[t] Set the local time zone info to
tzinfo
— for example, “PST8PDT”. Actually, if this is
not set, the TZ environment variable is cleared (so the system default is used); if set but
null, the user’s TZ variable is used, and if set and non-null the TZ variable is set to this
value.
TrustedUser=
user
The
user
parameter may be a user name (looked up in
/etc/passwd
) or a numeric user id.
Trusted user for file ownership and starting the daemon. If set, generated alias databases
and the control socket (if configured) will automatically be owned by this user.
TryNullMXList [w] If this system is the “best” (that is, lowest preference) MX for a given host, its configu-
ration rules should normally detect this situation and treat that condition specially by for-
warding the mail to a UUCP feed, treating it as local, or whatever. Howev er, in some cases
(such as Internet firewalls) you may want to try to connect directly to that host as though it
had no MX records at all. Setting this option causes
sendmail
to try this. The downside is
that errors in your configuration are likely to be diagnosed as “host unknown” or “message
timed out” instead of something more meaningful. This option is disrecommended.
UnixFromLine=
fromline
[$l macro] Defines the format used when
sendmail
must add a UNIX-style From_ line
(that is, a line beginning “From<space>user”). Defaults to “From $g $d”. Don’t change
this unless your system uses a different UNIX mailbox format (very unlikely).
UnsafeGroupWrites
If set (default), :include: and .forward files that are group writable are considered “unsafe”,
that is, they cannot reference programs or write directly to files. World writable :include:
and .forward files are always unsafe. Note: use
DontBlameSendmail
instead; this option
is deprecated.
UseCompressedIPv6Addresses
If set, the compressed format of IPv6 addresses, such as IPV6:::1, will be used, instead of
the uncompressed format, such as IPv6:0:0:0:0:0:0:0:1.
Sendmail Installation and Operation Guide
SMM:08-79
UseErrorsTo
[l] If there is an “Errors-To:” header, send error messages to the addresses listed there.
They normally go to the envelope sender. Use of this option causes
sendmail
to violate
RFC 1123. This option is disrecommended and deprecated.
UserDatabaseSpec=
udbspec
[U] The user database specification.
Verbose [v] Run in verbose mode. If this is set,
sendmail
adjusts options
HoldExpensive
(old
c
)
and
DeliveryMode
(old
d
) so that all mail is delivered completely in a single job so that
you can see the entire delivery process. Option
Verbose
should
never
be set in the config-
uration file; it is intended for command line use only. Note that the use of option
Verbose
can cause authentication information to leak, if you use a sendmail client to authenticate to
a server. If the authentication mechanism uses plain text passwords (as with LOGIN or
PLAIN), then the password could be compromised. To avoid this, do not install sendmail
set-user-ID root, and disable the
VERB
SMTP command with a suitable
PrivacyOptions
setting.
XscriptFileBufferSize=
threshold
Set the
threshold
, in bytes, before a memory-based queue transcript file becomes disk-
based. The default is 4096 bytes.
All options can be specified on the command line using the −O or −o flag, but most will cause
sendmail
to
relinquish its set-user-ID permissions. The options that will not cause this are SevenBitInput [7], EightBit-
Mode [8], MinFreeBlocks [b], CheckpointInterval [C], DeliveryMode [d], ErrorMode [e], IgnoreDots [i],
SendMimeErrors [j], LogLevel [L], MeToo [m], OldStyleHeaders [o], PrivacyOptions [p], SuperSafe [s],
Verbose [v], QueueSortOrder, MinQueueAge, DefaultCharSet, Dial Delay, NoRecipientAction, ColonOkI-
nAddr, MaxQueueRunSize, SingleLineFromHeader, and AllowBogusHELO. Actually, PrivacyOptions [p]
given on the command line are added to those already specified in the
sendmail.cf
file, i.e., they can’t be re-
set. Also, M (define macro) when defining the r or s macros is also considered “safe”.
5.8. P — Precedence Definitions
Values for the “Precedence:” field may be defined using the
P
control line. The syntax of this field is:
P
name
=
num
When the
name
is found in a “Precedence:” field, the message class is set to
num
. Higher numbers mean
higher precedence. Numbers less than zero have the special property that if an error occurs during process-
ing the body of the message will not be returned; this is expected to be used for “bulk” mail such as through
mailing lists. The default precedence is zero. For example, our list of precedences is:
Pfirst-class=0
Pspecial-delivery=100
Plist=−30
Pbulk=−60
Pjunk=−100
People writing mailing list exploders are encouraged to use “Precedence: list”. Older versions of
sendmail
(which discarded all error returns for negative precedences) didn’t recognize this name, giving it a default
precedence of zero. This allows list maintainers to see error returns on both old and new versions of
send-
.
5.9. V — Configuration Version Level
To provide compatibility with old configuration files, the
V
line has been added to define some very
basic semantics of the configuration file. These are not intended to be long term supports; rather, they de-
scribe compatibility features which will probably be removed in future releases.
N.B.:
these version
levels
have nothing to do with the version
number
on the files. For example, as of
this writing version 10 config files (specifically, 8.10) used version level 9 configurations.
SMM:08-80 Sendmail Installation and Operation Guide
“Old” configuration files are defined as version level one. Version level two files make the following
changes:
(1) Host name canonification ($[ ... $]) appends a dot if the name is recognized; this gives the config file
a way of finding out if anything matched. (Actually, this just initializes the “host” map with the “−a.”
flag — you can reset it to anything you prefer by declaring the map explicitly.)
(2) Default host name extension is consistent throughout processing; version level one configurations
turned off domain extension (that is, adding the local domain name) during certain points in process-
ing. Version level two configurations are expected to include a trailing dot to indicate that the name
is already canonical.
(3) Local names that are not aliases are passed through a new distinguished ruleset five; this can be used
to append a local relay. This behavior can be prevented by resolving the local name with an initial
‘@’. That is, something that resolves to a local mailer and a user name of “vikki” will be passed
through ruleset five, but a user name of “@vikki” will have the ‘@’ stripped, will not be passed
through ruleset five, but will otherwise be treated the same as the prior example. The expectation is
that this might be used to implement a policy where mail sent to “vikki” was handled by a central
hub, but mail sent to “vikki@localhost” was delivered directly.
Version level three files allow # initiated comments on all lines. Exceptions are backslash escaped #
marks and the $# syntax.
Version level four configurations are completely equivalent to level three for historical reasons.
Version level five configuration files change the default definition of
$w
to be just the first component
of the hostname.
Version level six configuration files change many of the local processing options (such as aliasing and
matching the beginning of the address for ‘|’ characters) to be mailer flags; this allows fine-grained control
over the special local processing. Level six configuration files may also use long option names. The
ColonOkInAddr
option (to allow colons in the local-part of addresses) defaults
on
for lower numbered con-
figuration files; the configuration file requires some additional intelligence to properly handle the RFC 822
group construct.
Version level sev en configuration files used new option names to replace old macros (
$e
became
SmtpGreetingMessage
,
$l
became
UnixFromLine
, and
$o
became
OperatorChars
. Also, prior to version
seven, the
F=q
flag (use 250 instead of 252 return value for
SMTP VRFY
commands) was assumed.
Version level eight configuration files allow
$#
on the left hand side of ruleset lines.
Version level nine configuration files allow parentheses in rulesets, i.e. they are not treated as com-
ments and hence removed.
Version level ten configuration files allow queue group definitions.
The
V
line may have an optional
/
vendor
to indicate that this configuration file uses modifications spe-
cific to a particular vendor
22
. You may use “/Berkeley” to emphasize that this configuration file uses the
Berkeley dialect of
sendmail
.
5.10. K — Key File Declaration
Special maps can be defined using the line:
Kmapname mapclass arguments
The
mapname
is the handle by which this map is referenced in the rewriting rules. The
mapclass
is the name
of a type of map; these are compiled in to
sendmail
. The
arguments
are interpreted depending on the class;
22
And of course, vendors are encouraged to add themselves to the list of recognized vendors by editing the routine
setvendor
in
conf.c
.
Please send e-mail to sendmail@Sendmail.ORG to register your vendor dialect.
Sendmail Installation and Operation Guide
SMM:08-81
typically, there would be a single argument naming the file containing the map.
Maps are referenced using the syntax:
$(
map key
$@
arguments
$:
default
$)
where either or both of the
arguments
or
default
portion may be omitted. The
$@ arguments
may appear
more than once. The indicated
key
and
arguments
are passed to the appropriate mapping function. If it re-
turns a value, it replaces the input. If it does not return a value and the
default
is specified, the
default
re-
places the input. Otherwise, the input is unchanged.
The
arguments
are passed to the map for arbitrary use. Most map classes can interpolate these argu-
ments into their values using the syntax “%
n
” (where
n
is a digit) to indicate the corresponding
argument
.
Argument “%0” indicates the database key. For example, the rule
R$− ! $+
$: $(uucp $1 $@ $2 $: $2 @ $1 . UUCP $)
looks up the UUCP name in a (user defined) UUCP map; if not found it turns it into “.UUCP” form. The
database might contain records like:
decvax %1@%0.DEC.COM
research %1@%0.ATT.COM
Note that
default
clauses never do this mapping.
The built-in map with both name and class “host” is the host name canonicalization lookup. Thus, the
syntax:
$(host
hostname
$)
is equivalent to:
$[
hostname
$]
There are many defined classes.
cdb Database lookups using the cdb(3) library.
Sendmail
must be compiled with
CDB
defined.
dbm Database lookups using the ndbm(3) library.
Sendmail
must be compiled with
NDBM
de-
fined.
btree Database lookups using the btree interface to the Berkeley DB library.
Sendmail
must be
compiled with
NEWDB
defined.
hash Database lookups using the hash interface to the Berkeley DB library.
Sendmail
must be
compiled with
NEWDB
defined.
nis NIS lookups.
Sendmail
must be compiled with
NIS
defined.
nisplus NIS+ lookups.
Sendmail
must be compiled with
NISPLUS
defined. The argument is the
name of the table to use for lookups, and the
−k
and
−v
flags may be used to set the key
and value columns respectively.
hesiod Hesiod lookups.
Sendmail
must be compiled with
HESIOD
defined.
ldap LDAP X500 directory lookups.
Sendmail
must be compiled with
LDAPMAP
defined.
The map supports most of the standard arguments and most of the command line argu-
ments of the
ldapsearch
program. Note that, by default, if a single query matches multiple
values, only the first value will be returned unless the
−z
(value separator) map option is
set. Also, the
−1
map flag will treat a multiple value return as if there were no matches.
netinfo NeXT NetInfo lookups.
Sendmail
must be compiled with
NETINFO
defined.
text Text file lookups. The format of the text file is defined by the
−k
(key field number),
−v
(value field number), and
−z
(field delimiter) options.
ph PH query map. Contributed and supported by Mark Roth, roth@uiuc.edu.
SMM:08-82 Sendmail Installation and Operation Guide
nsd nsd map for IRIX 6.5 and later. Contributed and supported by Bob Mende of SGI,
mende@sgi.com.
stab Internal symbol table lookups. Used internally for aliasing.
implicit Sequentially try a list of available map types:
hash
,
dbm
, and
cdb
. It is the default for alias
files if no class is specified. If is no matching map type is found, the text version is used
for the alias file, but other maps fail to open.
user Looks up users using
getpwnam
(3). The
−v
flag can be used to specify the name of the
field to return (although this is normally used only to check the existence of a user).
host Canonifies host domain names. Given a host name it calls the name server to find the
canonical name for that host.
bestmx Returns the best MX record for a host name given as the key. The current machine is al-
ways preferred — that is, if the current machine is one of the hosts listed as a lowest-pref-
erence MX record, then it will be guaranteed to be returned. This can be used to find out if
this machine is the target for an MX record, and mail can be accepted on that basis. If the
−z
option is given, then all MX names are returned, separated by the given delimiter. Note:
the return value is deterministic, i.e., even if multiple MX records have the same prefer-
ence, they will be returned in the same order.
dns This map requires the option -R to specify the DNS resource record type to lookup. The
following types are supported: A, AAAA, AFSDB, CNAME, MX, NS, PTR, SRV, and
TXT. A map lookup will return only one record unless the
−z
(value separator) option is
set. Hence for some types, e.g., MX records, the return value might be a random element
of the results due to randomizing in the DNS resolver, if only one element is returned.
arpa Returns the ‘‘reverse’’ for the given IP (IPv4 or IPv6) address, i.e., the string for the PTR
lookup, but without trailing
ip6.arpa
or
in-addr.arpa
. For example, the following config-
uration lines:
Karpa arpa
SArpa
R$+ $: $(arpa $1 $)
work like this in test mode:
sendmail -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
> Arpa IPv6:1:2:dead:beef:9876:0:0:1
Arpa input: IPv6 : 1 : 2 : dead : beef : 9876 : 0 : 0 : 1
Arpa returns: 1 . 0 . 0 . 0 . 0 . 0 . 0 . 0 . 0 . 0 . 0 . 0 . 6 . 7 . 8 . 9 . f . e . e . b . d . a . e . d . 2 . 0 . 0 . 0 . 1 . 0 . 0 . 0
> Arpa 1.2.3.4
Arpa input: 1 . 2 . 3 . 4
Arpa returns: 4 . 3 . 2 . 1
sequence The arguments on the ‘K’ line are a list of maps; the resulting map searches the argument
maps in order until it finds a match for the indicated key. For example, if the key definition
is:
Kmap1 ...
Kmap2 ...
Kseqmap sequence map1 map2
then a lookup against “seqmap” first does a lookup in map1. If that is found, it returns im-
mediately. Otherwise, the same key is used for map2.
syslog the key is logged via
syslogd
(8). The lookup returns the empty string.
Sendmail Installation and Operation Guide
SMM:08-83
switch Much like the “sequence” map except that the order of maps is determined by the service
switch. The argument is the name of the service to be looked up; the values from the ser-
vice switch are appended to the map name to create new map names. For example, con-
sider the key definition:
Kali switch aliases
together with the service switch entry:
aliases nis files
This causes a query against the map “ali” to search maps named “ali.nis” and “ali.files” in
that order.
dequote Strip double quotes (") from a name. It does not strip backslashes, and will not strip quotes
if the resulting string would contain unscannable syntax (that is, basic errors like unbal-
anced angle brackets; more sophisticated errors such as unknown hosts are not checked).
The intent is for use when trying to accept mail from systems such as DECnet that rou-
tinely quote odd syntax such as
"49ers::ubell"
A typical usage is probably something like:
Kdequote dequote
...
R$− $: $(dequote $1 $)
R$− $+
$: $>3 $1 $2
Care must be taken to prevent unexpected results; for example,
"|someprogram < input > output"
will have quotes stripped, but the result is probably not what you had in mind. Fortunately
these cases are rare.
regex
The map definition on the
K
line contains a regular expression. Any key input is compared
to that expression using the POSIX regular expressions routines regcomp(), regerr(), and
regexec(). Refer to the documentation for those routines for more information about the
regular expression matching. No rewriting of the key is done if the
−m
flag is used. With-
out it, the key is discarded or if
−s
if used, it is substituted by the substring matches, delim-
ited by
$|
or the string specified with the
−d
option. The options available for the map are
-n not
-f case sensitive
-b basic regular expressions (default is extended)
-s substring match
-d set the delimiter string used for -s
-a append string to key
-m match only, do not replace/discard value
-D perform no lookup in deferred delivery mode.
The
−s
option can include an optional parameter which can be used to select the substrings
in the result of the lookup. For example,
-s1,3,4
The delimiter string specified via the
−d
option is the sequence of characters after
d
ending
at the first space. Hence it isn’t possible to specify a space as delimiter, so if the option is
immediately followed by a space the delimiter string is empty, which means the substrings
are joined.
SMM:08-84 Sendmail Installation and Operation Guide
Notes: to match a
$
in a string, \$$ must be used. If the pattern contains spaces, they must
be replaced with the blank substitution character, unless it is space itself.
program The arguments on the
K
line are the pathname to a program and any initial parameters to
be passed. When the map is called, the key is added to the initial parameters and the pro-
gram is invoked as the default user/group id. The first line of standard output is returned as
the value of the lookup. This has many potential security problems, and has terrible perfor-
mance; it should be used only when absolutely necessary.
macro Set or clear a macro value. To set a macro, pass the value as the first argument in the map
lookup. To clear a macro, do not pass an argument in the map lookup. The map always re-
turns the empty string. Example of typical usage include:
Kstorage macro
...
# set macro ${MyMacro} to the ruleset match
R$+ $: $(storage {MyMacro} $@ $1 $) $1
# set macro ${MyMacro} to an empty string
R$* $: $(storage {MyMacro} $@ $) $1
# clear macro ${MyMacro}
R$− $: $(storage {MyMacro} $) $1
arith Perform simple arithmetic operations. The operation is given as key, currently +, -, *, /, %,
|, & (bitwise OR, AND), l (for less than), =, and r (for random) are supported. The two
operands are given as arguments. The lookup returns the result of the computation, i.e.,
TRUE
or
FALSE
for comparisons, integer values otherwise. The r operator returns a
pseudo-random number whose value lies between the first and second operand (which re-
quires that the first operand is smaller than the second). All options which are possible for
maps are ignored. A simple example is:
Kcomp arith
...
Scheck_etrn
R$* $: $(comp l $@ $&{load_avg} $@ 7 $) $1
RFALSE$# error ...
socket The socket map uses a simple request/reply protocol over TCP or UNIX domain sockets to
query an external server. Both requests and replies are text based and encoded as net-
strings, i.e., a string "hello there" becomes:
11:hello there,
Note: neither requests nor replies end with CRLF.
The request consists of the database map name and the lookup key separated by a space
character:
<mapname> ’ ’ <key>
The server responds with a status indicator and the result (if any):
Sendmail Installation and Operation Guide
SMM:08-85
<status> ’ ’ <result>
The status indicator specifies the result of the lookup operation itself and is one of the fol-
lowing upper case words:
OK the key was found, result contains the looked up value
NOTFOUNDthe key was not found, the result is empty
TEMP a temporary failure occurred
TIMEOUT a timeout occurred on the server side
PERM a permanent failure occurred
In case of errors (status TEMP, TIMEOUT or PERM) the result field may contain an ex-
planatory message. However, the explanatory message is not used any further by
send-
.
Example replies:
31:OK resolved.address@example.com,
56:OK error:550 5.7.1 User does not accept mail from sender,
in case of successful lookups, or:
8:NOTFOUND,
in case the key was not found, or:
55:TEMP this text explains that we had a temporary failure,
in case of a temporary map lookup failure.
The socket map uses the same syntax as milters (see Section "X — Mail Filter (Milter) De-
finitions") to specify the remote endpoint, e.g.,
Ksocket mySocketMap inet:12345@127.0.0.1
If multiple socket maps define the same remote endpoint, they will share a single connec-
tion to this endpoint.
Most of these accept as arguments the same optional flags and a filename (or a mapname for NIS; the
filename is the root of the database path, so that “.db” or some other extension appropriate for the database
type will be added to get the actual database name). Known flags are:
−o Indicates that this map is optional — that is, if it cannot be opened, no error is produced,
and
sendmail
will behave as if the map existed but was empty.
−N, −O
If neither
−N
or
−O
are specified,
sendmail
uses an adaptive algorithm to decide whether
or not to look for null bytes on the end of keys. It starts by trying both; if it finds any key
with a null byte it never tries again without a null byte and vice versa. If
−N
is specified it
never tries without a null byte and if
−O
is specified it never tries with a null byte. Setting
one of these can speed matches but are never necessary. If both
−N
and
−O
are specified,
sendmail
will never try any matches at all — that is, everything will appear to fail.
−a
x
Append the string
x
on successful matches. For example, the default
host
map appends a
dot on successful matches.
SMM:08-86 Sendmail Installation and Operation Guide
−T
x
Append the string
x
on temporary failures. For example,
x
would be appended if a DNS
lookup returned “server failed” or an NIS lookup could not locate a server. See also the
−t
flag.
−f Do not fold upper to lower case before looking up the key.
−m Match only (without replacing the value). If you only care about the existence of a key and
not the value (as you might when searching the NIS map “hosts.byname” for example),
this flag prevents the map from substituting the value. However, The −a argument is still
appended on a match, and the default is still taken if the match fails.
−k
keycol
The key column name (for NIS+) or number (for text lookups). For LDAP maps this is an
LDAP filter string in which %s is replaced with the literal contents of the lookup key and
%0 is replaced with the LDAP escaped contents of the lookup key according to RFC 2254.
If the flag
−K
is used, then %1 through %9 are replaced with the LDAP escaped contents
of the arguments specified in the map lookup.
−v
valcol
The value column name (for NIS+) or number (for text lookups). For LDAP maps this is
the name of one or more attributes to be returned; multiple attributes can be separated by
commas. If not specified, all attributes found in the match will be returned. The attributes
listed can also include a type and one or more objectClass values for matching as described
in the LDAP section.
−z
delim
The column delimiter (for text lookups). It can be a single character or one of the special
strings “ \n” or “ \t” to indicate newline or tab respectively. If omitted entirely, the column
separator is any sequence of white space. For LDAP and some other maps this is the sepa-
rator character to combine multiple values into a single return string. If not set, the LDAP
lookup will only return the first match found. For DNS maps this is the separator character
at which the result of a query is cut off if is too long.
−t Normally, when a map attempts to do a lookup and the server fails (e.g.,
sendmail
couldn’t
contact any name server; this is
not
the same as an entry not being found in the map), the
message being processed is queued for future processing. The
−t
flag turns off this behav-
ior, letting the temporary failure (server down) act as though it were a permanent failure
(entry not found). It is particularly useful for DNS lookups, where someone else’s miscon-
figured name server can cause problems on your machine. However, care must be taken to
ensure that you don’t bounce mail that would be resolved correctly if you tried again. A
common strategy is to forward such mail to another, possibly better connected, mail server.
−D Perform no lookup in deferred delivery mode. This flag is set by default for the
host
map.
−S
spacesub
The character to use to replace space characters after a successful map lookup (esp. useful
for regex and syslog maps).
−s
spacesub
For the dequote map only, the character to use to replace space characters after a successful
dequote.
−q Don’t dequote the key before lookup.
−L
level
For the syslog map only, it specifies the level to use for the syslog call.
−A When rebuilding an alias file, the
−A
flag causes duplicate entries in the text version to be
merged. For example, two entries:
list: user1, user2
list: user3
would be treated as though it were the single entry
list: user1, user2, user3
in the presence of the
−A
flag.
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Some additional flags are available for the host and dns maps:
−d delay: specify the resolver’s retransmission time interval (in seconds).
−r retry: specify the number of times to retransmit a resolver query.
The dns map has another flag:
−B basedomain: specify a domain that is always appended to queries.
Socket maps have an optional flag:
−d timeout: specify the timeout (in seconds) for communication with the socket map server.
The following additional flags are present in the ldap map only:
−c
timeout
Set the LDAP network timeout. sendmail must be compiled with
−DLDAP_OPT_NET-
WORK_TIMEOUT
to use this flag.
−R Do not auto chase referrals. sendmail must be compiled with
−DLDAP_REFERRALS
to
use this flag.
−n Retrieve attribute names only.
−V
sep
Retrieve both attributes name and value(s), separated by
sep
.
−r
deref
Set the alias dereference option to one of never, always, search, or find.
−s
scope
Set search scope to one of base, one (one level), or sub (subtree).
−h
host
LDAP server hostname. Some LDAP libraries allow you to specify multiple, space-sepa-
rated hosts for redundancy. In addition, each of the hosts listed can be followed by a colon
and a port number to override the default LDAP port.
−p
port
LDAP service port.
−H
LDAPURI
Use the specified LDAP URI instead of specifying the hostname and port separately with
the
−h
and
−p
options shown above. For example,
-h server.example.com -p 389 -b dc=example,dc=com
is equivalent to
-H ldap://server.example.com:389 -b dc=example,dc=com
If the LDAP library supports it, the LDAP URI format however can also request LDAP
over SSL by using
ldaps://
instead of
ldap://
. For example:
O LDAPDefaultSpec=-H ldaps://ldap.example.com -b dc=example,dc=com
Similarly, if the LDAP library supports it, It can also be used to specify a UNIX domain
socket using
ldapi://
:
O LDAPDefaultSpec=-H ldapi://socketfile -b dc=example,dc=com
−b
base
LDAP search base.
−l
timelimit
Time limit for LDAP queries.
−Z
sizelimit
Size (number of matches) limit for LDAP or DNS queries.
−d
distinguished_name
The distinguished name to use to login to the LDAP server.
−M
method
The method to authenticate to the LDAP server. Should be one of
LDAP_AUTH_NONE
,
LDAP_AUTH_SIMPLE
, or
LDAP_AUTH_KRBV4
. The leading
LDAP_AUTH_
can
be omitted and the value is case-insensitive.
−P
passwordfile
The file containing the secret key for the
LDAP_AUTH_SIMPLE
authentication method
or the name of the Kerberos ticket file for
LDAP_AUTH_KRBV4
.
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−1 Force LDAP searches to only succeed if a single match is found. If multiple values are
found, the search is treated as if no match was found.
−w
version
Set the LDAP API/protocol version to use. The default depends on the LDAP client li-
braries in use. For example,
−w 3
will cause
sendmail
to use LDAPv3 when communicat-
ing with the LDAP server.
−K Treat the LDAP search key as multi-argument and replace %1 through %9 in the key with
the LDAP escaped contents of the lookup arguments specified in the map lookup.
The
dbm
map appends the strings “.pag” and “.dir” to the given filename; the
hash
and
btree
maps ap-
pend “.db”. For example, the map specification
Kuucp dbm −o −N /etc/mail/uucpmap
specifies an optional map named “uucp” of class “dbm”; it always has null bytes at the end of every string,
and the data is located in /etc/mail/uucpmap.{dir,pag}.
The program
makemap
(8) can be used to build database-oriented maps. It takes at least the following
flags (for a complete list see its man page):
−f Do not fold upper to lower case in the map.
−N Include null bytes in keys.
−o Append to an existing (old) file.
−r Allow replacement of existing keys; normally, re-inserting an existing key is an error.
−v Print what is happening.
The
sendmail
daemon does not have to be restarted to read the new maps as long as you change them in
place; file locking is used so that the maps won’t be read while they are being updated.
New classes can be added in the routine
setupmaps
in file
conf.c
.
5.11. Q — Queue Group Declaration
In addition to the option
QueueDirectory,
queue groups can be declared that define a (group of) queue
directories under a common name. The syntax is as follows:
Q
name
{,
field
=
value
}+
where
name
is the symbolic name of the queue group under which it can be referenced in various places and
the “field=value” pairs define attributes of the queue group. The name must only consist of alphanumeric
characters. Fields are:
Flags Flags for this queue group.
Nice The nice(2) increment for the queue group. This value must be greater or equal zero.
Interval The time between two queue runs.
Path The queue directory of the group (required).
Runners The number of parallel runners processing the queue. Note that
F=f
must be set if this
value is greater than one.
Jobs The maximum number of jobs (messages delivered) per queue run.
recipients The maximum number of recipients per envelope. Envelopes with more than this number
of recipients will be split into multiple envelopes in the same queue directory. The default
value 0 means no limit.
Only the first character of the field name is checked.
By default, a queue group named
mqueue
is defined that uses the value of the
QueueDirectory
option
as path. Notice: all paths that are used for queue groups must be subdirectories of
QueueDirectory
. Since
they can be symbolic links, this isn’t a real restriction, If
QueueDirectory
uses a wildcard, then the directory
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SMM:08-89
one level up is considered the ‘‘base’’ directory which all other queue directories must share. Please make
sure that the queue directories do not overlap, e.g., do not specify
O QueueDirectory=/var/spool/mqueue/*
Qone, P=/var/spool/mqueue/dir1
Qtwo, P=/var/spool/mqueue/dir2
because this also includes “dir1” and “dir2” in the default queue group. However,
O QueueDirectory=/var/spool/mqueue/main*
Qone, P=/var/spool/mqueue/dir
Qtwo, P=/var/spool/mqueue/other*
is a valid queue group specification.
Options listed in the ‘‘Flags’’ field can be used to modify the behavior of a queue group. The ‘‘f ’’ flag
must be set if multiple queue runners are supposed to work on the entries in a queue group. Otherwise
send-
will work on the entries strictly sequentially.
The ‘‘Interval’’ field sets the time between queue runs. If no queue group specific interval is set, then
the parameter of the
-q
option from the command line is used.
To control the overall number of concurrently active queue runners the option
MaxQueueChildren
can be set. This limits the number of processes used for running the queues to
MaxQueueChildren
, though
at any one time fewer processes may be active as a result of queue options, completed queue runs, system
load, etc.
The maximum number of queue runners for an individual queue group can be controlled via the
Run-
ners
option. If set to 0, entries in the queue will not be processed, which is useful to ‘‘quarantine’’ queue
files. The number of runners per queue group may also be set with the option
MaxRunnersPerQueue
,
which applies to queue groups that have no individual limit. That is, the default value for
Runners
is
MaxRunnersPerQueue
if set, otherwise 1.
The field Jobs describes the maximum number of jobs (messages delivered) per queue run, which is
the queue group specific value of
MaxQueueRunSize
.
Notice: queue groups should be declared after all queue related options have been set because queue
groups take their defaults from those options. If an option is set after a queue group declaration, the values
of options in the queue group are set to the defaults of
sendmail
unless explicitly set in the declaration.
Each envelope is assigned to a queue group based on the algorithm described in section ‘‘Queue
Groups and Queue Directories’’.
5.12. X — Mail Filter (Milter) Definitions
The
sendmail
Mail Filter API (Milter) is designed to allow third-party programs access to mail mes-
sages as they are being processed in order to filter meta-information and content. They are declared in the
configuration file as:
X
name
{,
field
=
value
}*
where
name
is the name of the filter (used internally only) and the “field=name” pairs define attributes of the
filter. Also see the documentation for the
InputMailFilters
option for more information.
Fields are:
Socket The socket specification
Flags Special flags for this filter
Timeouts Timeouts for this filter
Only the first character of the field name is checked (it’s case-sensitive).
The socket specification is one of the following forms:
SMM:08-90 Sendmail Installation and Operation Guide
S=inet:
port
@
host
S=inet6:
port
@
host
S=local:
path
The first two describe an IPv4 or IPv6 socket listening on a certain
port
at a given
host
or IP address. The fi-
nal form describes a named socket on the filesystem at the given
path
.
The following flags may be set in the filter description.
R
Reject connection if filter unavailable.
T
Temporary fail connection if filter unavailable.
4
Drop connection with a 421 error if filter unavailable.
If none of these flags is specified, the message is passed through
sendmail
in case of filter errors as if
the failing filters were not present.
The timeouts can be set using the four fields inside of the
T=
equate:
C
Timeout for connecting to a filter. If set to 0, the system’s
connect()
timeout will be used.
S
Timeout for sending information from the MTA to a filter.
R
Timeout for reading reply from the filter.
E
Overall timeout between sending end-of-message to filter and waiting for the final acknowledgment.
Note the separator between each timeout field is a
’;’
. The default values (if not set) are:
T=C:5m;S:10s;R:10s;E:5m
where
s
is seconds and
m
is minutes.
Examples:
Xfilter1, S=local:/var/run/f1.sock, F=R
Xfilter2, S=inet6:999@localhost, F=T, T=S:1s;R:1s;E:5m
Xfilter3, S=inet:3333@localhost, T=C:2m
5.13. The User Database
The user database is deprecated in favor of ‘‘virtusertable’’ and ‘‘genericstable’’ as explained in the file
cf/README
. If you have a version of
sendmail
with the user database package compiled in, the handling
of sender and recipient addresses is modified.
The location of this database is controlled with the
UserDatabaseSpec
option.
5.13.1. Structure of the user database
The database is a sorted (BTree-based) structure. User records are stored with the key:
user-name
:
field-name
The sorted database format ensures that user records are clustered together. Meta-information is always
stored with a leading colon.
Field names define both the syntax and semantics of the value. Defined fields include:
maildrop The delivery address for this user. There may be multiple values of this record. In par-
ticular, mailing lists will have one
maildrop
record for each user on the list.
mailname The outgoing mailname for this user. For each outgoing name, there should be an ap-
propriate
maildrop
record for that name to allow return mail. See also
:default:mail-
name
.
mailsender Changes any mail sent to this address to have the indicated envelope sender. This is in-
tended for mailing lists, and will normally be the name of an appropriate -request ad-
dress. It is very similar to the owner-
list
syntax in the alias file.
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SMM:08-91
fullname The full name of the user.
office-address The office address for this user.
office-phone The office phone number for this user.
office-fax The office FAX number for this user.
home-address The home address for this user.
home-phone The home phone number for this user.
home-fax The home FAX number for this user.
project A (short) description of the project this person is affiliated with. In the University this
is often just the name of their graduate advisor.
plan A pointer to a file from which plan information can be gathered.
As of this writing, only a few of these fields are actually being used by
sendmail
:
maildrop
and
mailname
. A
finger
program that uses the other fields is planned.
5.13.2. User database semantics
When the rewriting rules submit an address to the local mailer, the user name is passed through the
alias file. If no alias is found (or if the alias points back to the same address), the name (with “:maildrop”
appended) is then used as a key in the user database. If no match occurs (or if the maildrop points at the
same address), forwarding is tried.
If the first token of the user name returned by ruleset 0 is an “@” sign, the user database lookup is
skipped. The intent is that the user database will act as a set of defaults for a cluster (in our case, the
Computer Science Division); mail sent to a specific machine should ignore these defaults.
When mail is sent, the name of the sending user is looked up in the database. If that user has a
“mailname” record, the value of that record is used as their outgoing name. For example, I might have a
record:
eric:mailname Eric.Allman@CS.Berkeley.EDU
This would cause my outgoing mail to be sent as Eric.Allman.
If a “maildrop” is found for the user, but no corresponding “mailname” record exists, the record
“:default:mailname” is consulted. If present, this is the name of a host to override the local host. For ex-
ample, in our case we would set it to “CS.Berkeley.EDU”. The effect is that anyone known in the data-
base gets their outgoing mail stamped as “user@CS.Berkeley.EDU”, but people not listed in the database
use the local hostname.
5.13.3. Creating the database
23
The user database is built from a text file using the
makemap
utility (in the distribution in the
makemap subdirectory). The text file is a series of lines corresponding to userdb records; each line has a
key and a value separated by white space. The key is always in the format described above — for exam-
ple:
eric:maildrop
This file is normally installed in a system directory; for example, it might be called
/etc/mail/userdb
. To
make the database version of the map, run the program:
makemap btree /etc/mail/userdb < /etc/mail/userdb
23
These instructions are known to be incomplete. Other features are available which provide similar functionality, e.g., virtual hosting and
mapping local addresses into a generic form as explained in cf/README.
SMM:08-92 Sendmail Installation and Operation Guide
Then create a config file that uses this. For example, using the V8 M4 configuration, include the follow-
ing line in your .mc file:
define(`confUSERDB_SPEC´, /etc/mail/userdb)
6. OTHER CONFIGURATION
There are some configuration changes that can be made by recompiling
sendmail
. This section describes
what changes can be made and what has to be modified to make them. In most cases this should be unnecessary
unless you are porting
sendmail
to a new environment.
6.1. Parameters in devtools/OS/$oscf
These parameters are intended to describe the compilation environment, not site policy, and should
normally be defined in the operating system configuration file.
This section needs a complete rewrite.
NDBM If set, the new version of the DBM library that allows multiple databases will be used. If
neither CDB, NDBM, nor NEWDB are set, a much less efficient method of alias lookup is
used.
CDB If set, use the cdb (tinycdb) package.
NEWDB If set, use the new database package from Berkeley (from 4.4BSD). This package is sub-
stantially faster than DBM or NDBM. If NEWDB and NDBM are both set,
sendmail
will
read DBM files, but will create and use NEWDB files.
NIS Include support for NIS. If set together with
both
NEWDB and NDBM,
sendmail
will
create both DBM and NEWDB files if and only if an alias file includes the substring “/yp/”
in the name. This is intended for compatibility with Sun Microsystems’
mkalias
program
used on YP masters.
NISPLUS Compile in support for NIS+.
NETINFO Compile in support for NetInfo (NeXT stations).
LDAPMAP Compile in support for LDAP X500 queries. Requires libldap and liblber from the Umich
LDAP 3.2 or 3.3 release or equivalent libraries for other LDAP libraries such as OpenL-
DAP.
HESIOD Compile in support for Hesiod.
MAP_NSD Compile in support for IRIX NSD lookups.
MAP_REGEX Compile in support for regular expression matching.
DNSMAP Compile in support for DNS map lookups in the
sendmail.cf
file.
PH_MAP Compile in support for ph lookups.
SASL Compile in support for SASL, a required component for SMTP Authentication support.
STARTTLS Compile in support for STARTTLS.
EGD Compile in support for the "Entropy Gathering Daemon" to provide better random data for
TLS.
TCPWRAPPERS Compile in support for TCP Wrappers.
_PATH_SENDMAILCF
The pathname of the sendmail.cf file.
_PATH_SENDMAILPID
The pathname of the sendmail.pid file.
SM_CONF_SHM
Compile in support for shared memory, see section about "/var/spool/mqueue".
Sendmail Installation and Operation Guide
SMM:08-93
MILTER Compile in support for contacting external mail filters built with the Milter API.
There are also several compilation flags to indicate the environment such as “_AIX3” and
“_SCO_unix_”. See the sendmail/README file for the latest scoop on these flags.
6.1.1. For Future Releases
sendmail
often contains compile time options
For Future Releases
(prefix _FFR_) which might be
enabled in a subsequent version or might simply be removed as they turned out not to be really useful.
These features are usually not documented but if they are, then the required (FFR) compile time options
are listed here for rulesets and macros, and in
cf/README
for mc/cf options. FFR compile times options
must be enabled when the sendmail binary is built from source. Enabled FFRs in a binary can be listed
with
sendmail -d0.13 < /dev/null | grep FFR
6.2. Parameters in sendmail/conf.h
Parameters and compilation options are defined in conf.h. Most of these need not normally be
tweaked; common parameters are all in sendmail.cf. However, the sizes of certain primitive vectors, etc., are
included in this file. The numbers following the parameters are their default value.
This document is not the best source of information for compilation flags in conf.h — see send-
mail/README or sendmail/conf.h itself.
MAXLINE [2048]
The maximum line length of any input line. If message lines exceed this length they
will still be processed correctly; however, header lines, configuration file lines, alias
lines, etc., must fit within this limit.
MAXNAME [256] The maximum length of any name, such as a host or a user name.
MAXPV [256]
The maximum number of parameters to any mailer. This limits the number of recipi-
ents that may be passed in one transaction. It can be set to any arbitrary number above
about 10, since
sendmail
will break up a delivery into smaller batches as needed. A
higher number may reduce load on your system, however.
MAXQUEUEGROUPS [50]
The maximum number of queue groups.
MAXATOM [1000] The maximum number of atoms (tokens) in a single address. For example, the address
“eric@CS.Berkeley.EDU” is seven atoms.
MAXMAILERS [25]The maximum number of mailers that may be defined in the configuration file. This
value is defined in include/sendmail/sendmail.h.
MAXRWSETS [200]The maximum number of rewriting sets that may be defined. The first half of these are
reserved for numeric specification (e.g., ‘‘S92’’), while the upper half are reserved for
auto-numbering (e.g., ‘‘Sfoo’’). Thus, with a value of 200 an attempt to use ‘‘S99’’ will
succeed, but ‘‘S100’’ will fail.
MAXPRIORITIES [25]
The maximum number of values for the “Precedence:” field that may be defined (using
the
P
line in sendmail.cf).
MAXUSERENVIRON [100]
The maximum number of items in the user environment that will be passed to subordi-
nate mailers.
MAXMXHOSTS [100]
The maximum number of MX records we will accept for any single host.
MAXMAPSTACK [12]
The maximum number of maps that may be "stacked" in a
sequence
class map.
SMM:08-94 Sendmail Installation and Operation Guide
MAXMIMEARGS [20]
The maximum number of arguments in a MIME Content-Type: header; additional argu-
ments will be ignored.
MAXMIMENESTING [20]
The maximum depth to which MIME messages may be nested (that is, nested Message
or Multipart documents; this does not limit the number of components in a single Mul-
tipart document).
MAXDAEMONS [10]
The maximum number of sockets sendmail will open for accepting connections on dif-
ferent ports.
MAXMACNAMELEN [25]
The maximum length of a macro name.
A number of other compilation options exist. These specify whether or not specific code should be compiled
in. Ones marked with † are 0/1 valued.
NETINET† If set, support for Internet protocol networking is compiled in. Previous versions of
sendmail
referred to this as
DAEMON
; this old usage is now incorrect. Defaults on;
turn it off in the Makefile if your system doesn’t support the Internet protocols.
NETINET6† If set, support for IPv6 networking is compiled in. It must be separately enabled by
adding
DaemonPortOptions
settings.
NETISO† If set, support for ISO protocol networking is compiled in (it may be appropriate to
#define this in the Makefile instead of conf.h).
NETUNIX† If set, support for UNIX domain sockets is compiled in. This is used for control socket
support.
LOG If set, the
syslog
routine in use at some sites is used. This makes an informational log
record for each message processed, and makes a higher priority log record for internal
system errors.
STRONGLY RECOMMENDED
— if you want no logging, turn it off
in the configuration file.
MATCHGECOS† Compile in the code to do ‘‘fuzzy matching’’ on the GECOS field in /etc/passwd. This
also requires that the
MatchGECOS
option be turned on.
NAMED_BIND† Compile in code to use the Berkeley Internet Name Domain (BIND) server to resolve
TCP/IP host names.
NOTUNIX If you are using a non-UNIX mail format, you can set this flag to turn off special pro-
cessing of UNIX-style “From ” lines.
USERDB† Include the
experimental
Berkeley user information database package. This adds a
new lev el of local name expansion between aliasing and forwarding. It also uses the
NEWDB package. This may change in future releases.
The following options are normally turned on in per-operating-system clauses in conf.h.
IDENTPROT O†
Compile in the IDENT protocol as defined in RFC 1413. This defaults on for all sys-
tems except Ultrix, which apparently has the interesting “feature” that when it receives
a “host unreachable” message it closes all open connections to that host. Since some
firewall gateways send this error code when you access an unauthorized port (such as
113, used by IDENT), Ultrix cannot receive email from such hosts.
SYSTEM5 Set all of the compilation parameters appropriate for System V.
HASFLOCK† Use Berkeley-style
flock
instead of System V
lockf
to do file locking. Due to the
highly unusual semantics of locks across forks in
lockf
, this should always be used if at
all possible.
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HASINITGROUPS Set this if your system has the
initgroups()
call (if you have multiple group support).
This is the default if SYSTEM5 is
not
defined or if you are on HPUX.
HASUNAME Set this if you have the
uname
(2) system call (or corresponding library routine). Set by
default if SYSTEM5 is set.
HASGETDTABLESIZE
Set this if you have the
getdtablesize
(2) system call.
HASWAITPID Set this if you have the
haswaitpid
(2) system call.
FAST_PID_RECYCLE
Set this if your system can possibly reuse the same pid in the same second of time.
SFS_TYPE The mechanism that can be used to get file system capacity information. The values
can be one of SFS_USTAT (use the ustat(2) syscall), SFS_4ARGS (use the four argu-
ment statfs(2) syscall), SFS_VFS (use the two argument statfs(2) syscall including
<sys/vfs.h>), SFS_MOUNT (use the two argument statfs(2) syscall including
<sys/mount.h>), SFS_STATFS (use the two argument statfs(2) syscall including
<sys/statfs.h>), SFS_STATVFS (use the two argument statfs(2) syscall including
<sys/statvfs.h>), or SFS_NONE (no way to get this information).
LA_TYPE The load average type. Details are described below.
The are several built-in ways of computing the load average.
Sendmail
tries to auto-configure them based on
imperfect guesses; you can select one using the
cc
option
−DLA_TYPE=
type
, where
type
is:
LA_INT The kernel stores the load average in the kernel as an array of long integers. The actual
values are scaled by a factor FSCALE (default 256).
LA_SHORT
The kernel stores the load average in the kernel as an array of short integers. The actual
values are scaled by a factor FSCALE (default 256).
LA_FLOAT The kernel stores the load average in the kernel as an array of double precision floats.
LA_MACH Use MACH-style load averages.
LA_SUBR Call the
getloadavg
routine to get the load average as an array of doubles.
LA_ZERO
Always return zero as the load average. This is the fallback case.
If type
LA_INT
,
LA_SHORT
, or
LA_FLOAT
is specified, you may also need to specify
_PATH_UNIX
(the path
to your system binary) and
LA_AVENRUN
(the name of the variable containing the load average in the ker-
nel; usually “_avenrun” or “avenrun”).
6.3. Configuration in sendmail/conf.c
The following changes can be made in conf.c.
6.3.1. Built-in Header Semantics
Not all header semantics are defined in the configuration file. Header lines that should only be in-
cluded by certain mailers (as well as other more obscure semantics) must be specified in the
HdrInfo
ta-
ble in
conf.c
. This table contains the header name (which should be in all lower case) and a set of header
control flags (described below), The flags are:
H_ACHECK Normally when the check is made to see if a header line is compatible with a
mailer,
sendmail
will not delete an existing line. If this flag is set,
sendmail
will
delete even existing header lines. That is, if this bit is set and the mailer does not
have flag bits set that intersect with the required mailer flags in the header definition
in sendmail.cf, the header line is
always
deleted.
H_EOH If this header field is set, treat it like a blank line, i.e., it will signal the end of the
header and the beginning of the message text.
SMM:08-96 Sendmail Installation and Operation Guide
H_FORCE Add this header entry even if one existed in the message before. If a header entry
does not have this bit set,
sendmail
will not add another header line if a header line
of this name already existed. This would normally be used to stamp the message by
ev eryone who handled it.
H_TRACE If set, this is a timestamp (trace) field. If the number of trace fields in a message ex-
ceeds a preset amount the message is returned on the assumption that it has an
aliasing loop.
H_RCPT If set, this field contains recipient addresses. This is used by the
−t
flag to deter-
mine who to send to when it is collecting recipients from the message.
H_FROM This flag indicates that this field specifies a sender. The order of these fields in the
HdrInfo
table specifies
sendmail
’s preference for which field to return error mes-
sages to.
H_ERRORSTO
Addresses in this header should receive error messages.
H_CTE This header is a Content-Transfer-Encoding header.
H_CTYPE This header is a Content-Type header.
H_BCC Strip the value from the header (for Bcc:).
Let’s look at a sample
HdrInfo
specification:
struct hdrinfo
HdrInfo[] =
{
/* originator fields, most to least significant */
"resent-sender", H_FROM,
"resent-from", H_FROM,
"sender", H_FROM,
"from", H_FROM,
"full-name", H_ACHECK,
"errors-to", H_FROM | H_ERRORSTO,
/* destination fields */
"to", H_RCPT,
"resent-to", H_RCPT,
"cc", H_RCPT,
"bcc", H_RCPT|H_BCC,
/* message identification and control */
"message", H_EOH,
"text", H_EOH,
/* trace fields */
"received", H_TRACE | H_FORCE,
/* miscellaneous fields */
"content-transfer-encoding", H_CTE,
"content-type", H_CTYPE,
NULL, 0,
};
This structure indicates that the “To:”, “Resent-To:”, and “Cc:” fields all specify recipient addresses.
Any “Full-Name:” field will be deleted unless the required mailer flag (indicated in the configuration file)
is specified. The “Message:” and “Text:” fields will terminate the header; these are used by random dis-
senters around the network world. The “Received:” field will always be added, and can be used to trace
messages.
There are a number of important points here. First, header fields are not added automatically just
because they are in the
HdrInfo
structure; they must be specified in the configuration file in order to be
Sendmail Installation and Operation Guide
SMM:08-97
added to the message. Any header fields mentioned in the configuration file but not mentioned in the
HdrInfo
structure have default processing performed; that is, they are added unless they were in the mes-
sage already. Second, the
HdrInfo
structure only specifies cliched processing; certain headers are
processed specially by ad hoc code regardless of the status specified in
HdrInfo
. For example, the
“Sender:” and “From:” fields are always scanned on ARPANET mail to determine the sender
24
; this is
used to perform the “return to sender” function. The “From:” and “Full-Name:” fields are used to deter-
mine the full name of the sender if possible; this is stored in the macro
$x
and used in a number of ways.
6.3.2. Restricting Use of Email
If it is necessary to restrict mail through a relay, the
checkcompat
routine can be modified. This
routine is called for every recipient address. It returns an exit status indicating the status of the message.
The status
EX_OK
accepts the address,
EX_TEMPFAIL
queues the message for a later try, and other values
(commonly
EX_UNAVAILABLE
) reject the message. It is up to
checkcompat
to print an error message
(using
usrerr
) if the message is rejected. For example,
checkcompat
could read:
int
checkcompat(to, e)
register ADDRESS *to;
register ENVELOPE *e;
{
register STAB *s;
s = stab("private", ST_MAILER, ST_FIND);
if (s != NULL && e−>e_from.q_mailer != LocalMailer &&
to->q_mailer == s->s_mailer)
{
usrerr("No private net mail allowed through this machine");
return (EX_UNAVAILABLE);
}
if (MsgSize > 50000 && bitnset(M_LOCALMAILER, to−>q_mailer))
{
usrerr("Message too large for non-local delivery");
e−>e_flags |= EF_NORETURN;
return (EX_UNAVAILABLE);
}
return (EX_OK);
}
This would reject messages greater than 50000 bytes unless they were local. The
EF_NORETURN
flag
can be set in
e
→
e_flags
to suppress the return of the actual body of the message in the error return. The
actual use of this routine is highly dependent on the implementation, and use should be limited.
6.3.3. New Database Map Classes
New key maps can be added by creating a class initialization function and a lookup function.
These are then added to the routine
setupmaps.
The initialization function is called as
xxx
_map_init(MAP *map, char *args)
The
map
is an internal data structure. The
args
is a pointer to the portion of the configuration file line
following the map class name; flags and filenames can be extracted from this line. The initialization
function must return
true
if it successfully opened the map,
false
otherwise.
24
Actually, this is no longer true in SMTP; this information is contained in the envelope. The older ARPANET protocols did not complete-
ly distinguish envelope from header.
SMM:08-98 Sendmail Installation and Operation Guide
The lookup function is called as
xxx
_map_lookup(MAP *map, char buf[], char **av, int *statp)
The
map
defines the map internally. The
buf
has the input key. This may be (and often is) used destruc-
tively. The
av
is a list of arguments passed in from the rewrite line. The lookup function should return a
pointer to the new value. If the map lookup fails,
*statp
should be set to an exit status code; in particular,
it should be set to
EX_TEMPFAIL
if recovery is to be attempted by the higher level code.
6.3.4. Queueing Function
The routine
shouldqueue
is called to decide if a message should be queued or processed immedi-
ately. Typically this compares the message priority to the current load average. The default definition is:
bool
shouldqueue(pri, ctime)
long pri;
time_t ctime;
{
if (CurrentLA < QueueLA)
return false;
return (pri > (QueueFactor / (CurrentLA − QueueLA + 1)));
}
If the current load average (global variable
CurrentLA
, which is set before this function is called) is less
than the low threshold load average (option
x
, variable
QueueLA
),
shouldqueue
returns
false
immediately
(that is, it should
not
queue). If the current load average exceeds the high threshold load average (option
X
, variable
RefuseLA
),
shouldqueue
returns
true
immediately. Otherwise, it computes the function based
on the message priority, the queue factor (option
q
, global variable
QueueFactor
), and the current and
threshold load averages.
An implementation wishing to take the actual age of the message into account can also use the
ctime
parameter, which is the time that the message was first submitted to
sendmail
. Note that the
pri
parameter is already weighted by the number of times the message has been tried (although this tends to
lower the priority of the message with time); the expectation is that the
ctime
would be used as an “es-
cape clause” to ensure that messages are eventually processed.
6.3.5. Refusing Incoming SMTP Connections
The function
refuseconnections
returns
true
if incoming SMTP connections should be refused. The
current implementation is based exclusively on the current load average and the refuse load average op-
tion (option
X
, global variable
RefuseLA
):
bool
refuseconnections()
{
return (RefuseLA > 0 && CurrentLA >= RefuseLA);
}
A more clever implementation could look at more system resources.
6.3.6. Load Av erage Computation
The routine
getla
returns the current load average (as a rounded integer). The distribution includes
several possible implementations. If you are porting to a new environment you may need to add some
Sendmail Installation and Operation Guide
SMM:08-99
new tweaks.
25
6.4. Configuration in sendmail/daemon.c
The file
sendmail/daemon.c
contains a number of routines that are dependent on the local networking
environment. The version supplied assumes you have BSD style sockets.
In previous releases, we recommended that you modify the routine
maphostname
if you wanted to
generalize
$[
...
$]
lookups. We now recommend that you create a new keyed map instead.
6.5. LDAP
In this section we assume that
sendmail
has been compiled with support for LDAP.
6.5.1. LDAP Recursion
LDAP Recursion allows you to add types to the search attributes on an LDAP map specification.
The syntax is:
−v
ATTRIBUTE
[:
TYPE
[:
OBJECTCLASS
[|
OBJECTCLASS
|...]]]
The new
TYPE
s are:
NORMAL This attribute type specifies the attribute to add to the results string. This is the default.
DN Any matches for this attribute are expected to have a value of a fully qualified distin-
guished name.
sendmail
will lookup that DN and apply the attributes requested to the
returned DN record.
FILTER Any matches for this attribute are expected to have a value of an LDAP search filter.
sendmail
will perform a lookup with the same parameters as the original search but re-
places the search filter with the one specified here.
URL Any matches for this attribute are expected to have a value of an LDAP URL.
send-
will perform a lookup of that URL and use the results from the attributes named in
that URL. Note however that the search is done using the current LDAP connection,
regardless of what is specified as the scheme, LDAP host, and LDAP port in the LDAP
URL.
Any untyped attributes are considered
NORMAL
attributes as described above.
The optional
OBJECTCLASS
(| separated) list contains the objectClass values for which that at-
tribute applies. If the list is given, the attribute named will only be used if the LDAP record being re-
turned is a member of that object class. Note that if these new value attribute
TYPE
s are used in an
AliasFile option setting, it will need to be double quoted to prevent
sendmail
from misparsing the colons.
Note that LDAP recursion attributes which do not ultimately point to an LDAP record are not con-
sidered an error.
6.5.1.1. Example
Since examples usually help clarify, here is an example which uses all four of the new types:
25
If you do, please send updates to sendmail@Sendmail.ORG.
SMM:08-100 Sendmail Installation and Operation Guide
O LDAPDefaultSpec=-h ldap.example.com -b dc=example,dc=com
Ke xample ldap
-z,
-k (&(objectClass=sendmailMTAAliasObject)(sendmailMTAKey=%0))
-v sendmailMTAAliasValue,mail:NORMAL:inetOrgPerson,
uniqueMember:DN:groupOfUniqueNames,
sendmailMTAAliasSearch:FILTER:sendmailMTAAliasObject,
sendmailMTAAliasURL:URL:sendmailMTAAliasObject
That definition specifies that:
• Any value in a
sendmailMTAAliasValue
attribute will be added to the result string regardless of ob-
ject class.
• The
attribute will be added to the result string if the LDAP record is a member of the
inetOrg-
Person
object class.
• The
uniqueMember
attribute is a recursive attribute, used only in
groupOfUniqueNames
records, and
should contain an LDAP DN pointing to another LDAP record. The desire here is to return the
attribute from those DNs.
• The
sendmailMTAAliasSearch
attribute and
sendmailMTAAliasURL
are both used only if referenced
in a
sendmailMTAAliasObject
. They are both recursive, the first for a new LDAP search string and
the latter for an LDAP URL.
6.6. STARTTLS
In this section we assume that
sendmail
has been compiled with support for STARTTLS. To properly
understand the use of STARTTLS in
sendmail
, it is necessary to understand at least some basics about X.509
certificates and public key cryptography. This information can be found in books about SSL/TLS or on
WWW sites, e.g., “https://www.OpenSSL.org/”.
6.6.1. Certificates for STARTTLS
When acting as a server,
sendmail
requires X.509 certificates to support STARTTLS: one as certifi-
cate for the server (ServerCertFile and corresponding private ServerKeyFile) at least one root CA (CAC-
ertFile), i.e., a certificate that is used to sign other certificates, and a path to a directory which contains
(zero or more) other CAs (CACertPath). The file specified via CACertFile can contain several certifi-
cates of CAs. The DNs of these certificates are sent to the client during the TLS handshake (as part of
the CertificateRequest) as the list of acceptable CAs. However, do not list too many root CAs in that file,
otherwise the TLS handshake may fail; e.g.,
error:14094417:SSL routines:SSL3_READ_BYTES:
sslv3 alert illegal parameter:s3_pkt.c:964:SSL alert number 47
You should probably put only the CA cert into that file that signed your own cert(s), or at least only those
you trust. The CACertPath directory must contain the hashes of each CA certificate as filenames (or as
links to them). Symbolic links can be generated with the following two (Bourne) shell commands:
C=FileName_of_CA_Certificate
ln -s $C ‘openssl x509 -noout -hash < $C‘.0
A better way to do this is to use the
c_rehash
command that is part of the OpenSSL distribution because
it handles subject hash collisions by incrementing the number in the suffix of the filename of the sym-
bolic link, e.g.,
.0
to
.1
, and so on. An X.509 certificate is also required for authentication in client mode
(ClientCertFile and corresponding private ClientKeyFile), however,
sendmail
will always use START-
TLS when offered by a server. The client and server certificates can be identical. Certificates can be ob-
tained from a certificate authority or created with the help of OpenSSL. The required format for certifi-
cates and private keys is PEM. To allow for automatic startup of sendmail, private keys (ServerKeyFile,
ClientKeyFile) must be stored unencrypted. The keys are only protected by the permissions of the file
Sendmail Installation and Operation Guide
SMM:08-101
system. Never make a private key available to a third party.
The options
ClientCertFile
,
ClientKeyFile
,
ServerCertFile
, and
ServerKeyFile
can take a second
file name, which must be separated from the first with a comma (note: do not use any spaces) to set up a
second cert/key pair. This can be used to have certs of different types, e.g., RSA and DSA.
6.6.2. PRNG for STARTTLS
STARTTLS requires a strong pseudo random number generator (PRNG) to operate properly. De-
pending on the TLS library you use, it may be required to explicitly initialize the PRNG with random
data. OpenSSL makes use of
/dev/urandom(4)
if available (this corresponds to the compile flag HA-
SURANDOMDEV). On systems which lack this support, a random file must be specified in the
send-
mail.cf
file using the option RandFile. It is
strongly
advised to use the "Entropy Gathering Daemon"
EGD from Brian Warner on those systems to provide useful random data. In this case,
sendmail
must be
compiled with the flag EGD, and the RandFile option must point to the EGD socket. If neither
/dev/urandom(4)
nor EGD are available, you have to make sure that useful random data is available all
the time in RandFile. If the file hasn’t been modified in the last 10 minutes before it is supposed to be
used by
sendmail
the content is considered obsolete. One method for generating this file is:
openssl rand -out /etc/mail/randfile -rand
/path/to/file:...
256
See the OpenSSL documentation for more information. In this case, the PRNG for TLS is only seeded
with other random data if the
DontBlameSendmail
option
InsufficientEntropy
is set. This is most
likely not sufficient for certain actions, e.g., generation of (temporary) keys.
Please see the OpenSSL documentation or other sources for further information about certificates,
their creation and their usage, the importance of a good PRNG, and other aspects of TLS.
6.7. Encoding of STARTTLS and AUTH related Macros
Macros that contain STARTTLS and AUTH related data which comes from outside sources, e.g., all
macros containing information from certificates, are encoded to avoid problems with non-printable or special
characters. The latter are ’\’, ’<’, ’>’, ’(’, ’)’, ’"’, ’+’, and ’ ’. All of these characters are replaced by their
value in hexadecimal with a leading ’+’. For example:
/C=US/ST=California/O=endmail.org/OU=private/CN=Darth Mail (Cert)/
Email=darth+cert@endmail.org
is encoded as:
/C=US/ST=California/O=endmail.org/OU=private/
CN=Darth+20Mail+20+28Cert+29/Email=darth+2Bcert@endmail.org
(line breaks have been inserted for readability). The macros which are subject to this encoding are
{cert_subject}, {cert_issuer}, {cn_subject}, {cn_issuer}, as well as {auth_authen} and {auth_author}.
6.8. DANE
Support for DANE (see RFC 7672 et.al.) is available if
sendmail
is compiled with the option
DANE
.
If OpenSSL 1.1.1 or at least 3.0.0 are used, then full DANE support for DANE-EE and DANE-TA (as re-
quired by RFC 7672) is available via the functions provided by those OpenSSL versions (run
sendmail -bt -d0.3 < /dev/null
and check that HAVE_SSL_CTX_dane_enable is in the output), otherwise support for TLSA RR 3-1-x is
implemented directly in
sendmail
. Note: if OpenSSL functions related to DANE cause a failure, then the
macro
${verify}
is set to
DANE_TEMP
. This also applies if TLS cannot be initialized at all. The option
O DANE=true
enables this feature at run time and it automatically adds
use_dnssec
and
use_edns0
to
SMM:08-102 Sendmail Installation and Operation Guide
O ResolverOptions
This requires a DNSSEC-validating recursive resolver which supports those options. The resolver must be
reachable via a trusted connection, hence it is best to run it locally.
If the client finds a usable TLSA RR and the check succeeds the macro
${verify}
is set to
TRUSTED
. All
non-DNS maps are considered
secure
just like DNS lookups with DNSSEC. Be aware that TLSA RRs are
not looked up for some features, e.g.,
FallBackSmartHost
.
6.9. EAI
Experimental support for SMTPUTF8 (EAI, see RFC 6530-6533) is available when the compile time
option
USE_EAI,
(see also
devtools/Site/site.config.m4.sample
for other settings that might be needed), and
the cf option
SMTPUTF8
are used. This allows the use of UTF-8 for envelope addresses as well as the entire
message. DNS lookups are done using the A-label format (Punycode) as required by the RFCs. For all other
interactions with external programs and maps, the actual value are used, i.e., no conversions between UTF-8
and ASCII encodings are made. This applies to the keys in map lookups, which might require to specify
both versions in a map; the data exchanged with a milter, i.e., each milter must be "8 bit clean"; mail delivery
agents which must be able to handle 8 bit addresses. Some values must be ASCII as those are used before
SMTPUTF8 support can be requested, e.g., the macros
$j
and
$m.
Please test and provide feedback.
6.10. MTA-STS
Experimental support for SMTP MTA Strict Transport Security (MTA-STS, see RFC 8461) is avail-
able when using the compile time option _FFR_MTA_STS (as well as some others, e.g., _FFR_TLS_ALT-
NAMES and obviously STARTTLS), FEATURE(sts) (which implicitly sets the cf option StrictTransportSe-
curity), and postfix-mta-sts-resolver (see https://github.com/Snawoot/postfix-mta-sts-resolver.git).
Note: this implementation uses a socket map to communicate with postfix-mta-sts-resolver and han-
dles only the values returned by that program, which might not fully implement MTA-STS.
If both DANE and MTA-STS are enabled and available for the receiving domain, DANE is used be-
cause it offers a much higher level of security.
7. ACKNOWLEDGEMENTS
I’ve worked on
sendmail
for many years, and many employers have been remarkably patient about letting
me work on a large project that was not part of my official job. This includes time on the INGRES Project at the
University of California at Berkeley, at Britton Lee, and again on the Mammoth and Titan Projects at Berkeley.
Much of the second wav e of improvements resulting in version 8.1 should be credited to Bryan Costales of
the International Computer Science Institute. As he passed me drafts of his book on
sendmail
I was inspired to
start working on things again. Bryan was also available to bounce ideas off of.
Gregory Neil Shapiro of Worcester Polytechnic Institute has become instrumental in all phases of
send-
support and development, and was largely responsible for getting versions 8.8 and 8.9 out the door.
Many, many people contributed chunks of code and ideas to
sendmail
. It has proven to be a group net-
work effort. Version 8 in particular was a group project. The following people and organizations made notable
contributions:
Claus Assmann
John Beck, Hewlett-Packard & Sun Microsystems
Keith Bostic, CSRG, University of California, Berkeley
Andrew Cheng, Sun Microsystems
Michael J. Corrigan, University of California, San Diego
Bryan Costales, International Computer Science Institute & InfoBeat
Pa
..
r (Pell) Emanuelsson
Craig Everhart, Transarc Corporation
Sendmail Installation and Operation Guide
SMM:08-103
Per Hedeland, Ericsson
Tom Ivar Helbekkmo, Norwegian School of Economics
Kari Hurtta, Finnish Meteorological Institute
Allan E. Johannesen, WPI
Jonathan Kamens, OpenVision Technologies, Inc.
Takahiro Kanbe, Fuji Xerox Information Systems Co., Ltd.
Brian Kantor, University of California, San Diego
John Kennedy, Cal State University, Chico
Murray S. Kucherawy, HookUp Communication Corp.
Bruce Lilly, Sony U.S.
Karl London
Motonori Nakamura, Ritsumeikan University & Kyoto University
John Gardiner Myers, Carnegie Mellon University
Neil Rickert, Northern Illinois University
Gregory Neil Shapiro, WPI
Eric Schnoebelen, Convex Computer Corp.
Eric Wassenaar, National Institute for Nuclear and High Energy Physics, Amsterdam
Randall Winchester, University of Maryland
Christophe Wolfhugel, Pasteur Institute & Herve Schauer Consultants (Paris)
Exactis.com, Inc.
I apologize for anyone I have omitted, misspelled, misattributed, or otherwise missed. At this point, I suspect
that at least a hundred people have contributed code, and many more have contributed ideas, comments, and en-
couragement. I’ve tried to list them in the RELEASE_NOTES in the distribution directory. I appreciate their
contribution as well.
Special thanks are reserved for Michael Corrigan and Christophe Wolfhugel, who besides being wonderful
guinea pigs and contributors have also consented to be added to the ‘‘sendmail@Sendmail.ORG’’ list and, by an-
swering the bulk of the questions sent to that list, have freed me up to do other work.
Appendix A
COMMAND LINE FLAGS
Arguments must be presented with flags before addresses. The flags are:
−A
x
Select an alternative .cf file which is either
sendmail.cf
for
−Am
or
submit.cf
for
−Ac
. By default
the .cf file is chosen based on the operation mode. For
-bm
(default),
-bs
, and
-t
it is
submit.cf
if
it exists, for all others it is
sendmail.cf
.
−b
x
Set operation mode to
x
. Operation modes are:
m
Deliver mail (default)
s
Speak SMTP on input side
a† ‘‘Arpanet’’ mode (get envelope sender information from header)
C
Check the configuration file
d
Run as a daemon in background
D
Run as a daemon in foreground
t
Run in test mode
v
Just verify addresses, don’t collect or deliver
i
Initialize the alias database
p
Print the mail queue
P
Print overview over the mail queue (requires shared memory)
h
Print the persistent host status database
H
Purge expired entries from the persistent host status database
−B
type
Indicate body type.
−C
file
Use a different configuration file.
Sendmail
runs as the invoking user (rather than root) when this
flag is specified.
−D
logfile
Send debugging output to the indicated
logfile
instead of stdout.
−d
level
Set debugging level.
−f
addr
The envelope sender address is set to
addr
. This address may also be used in the From: header if
that header is missing during initial submission. The envelope sender address is used as the recipi-
ent for delivery status notifications and may also appear in a Return-Path: header.
−F
name
Sets the full name of this user to
name
.
−G When accepting messages via the command line, indicate that they are for relay (gateway) submis-
sion. sendmail may complain about syntactically invalid messages, e.g., unqualified host names,
rather than fixing them when this flag is set. sendmail will not do any canonicalization in this
mode.
−h
cnt
Sets the “hop count” to
cnt
. This represents the number of times this message has been processed
by
sendmail
(to the extent that it is supported by the underlying networks).
Cnt
is incremented
during processing, and if it reaches MAXHOP (currently 25)
sendmail
throws away the message
with an error.
†Deprecated.
SMM:08-104 Sendmail Installation and Operation Guide
Sendmail Installation and Operation Guide
SMM:08-105
−L
tag
Sets the identifier used for syslog. Note that this identifier is set as early as possible. However,
sendmail
may be used if problems arise before the command line arguments are processed.
−n Don’t do aliasing or forwarding.
−N
notifications
Tag all addresses being sent as wanting the indicated
notifications
, which consists of the word
“NEVER” or a comma-separated list of “SUCCESS”, “FAILURE”, and “DELAY” for successful
delivery, failure, and a message that is stuck in a queue somewhere. The default is “FAIL-
URE,DELAY”.
−r
addr
An obsolete form of
−f
.
−o
x value
Set option
x
to the specified
value
. These options are described in Section 5.6.
−O
option
=
value
Set
option
to the specified
value
(for long form option names). These options are described in
Section 5.6.
−M
x value
Set macro
x
to the specified
value
.
−p
protocol
Set the sending protocol. Programs are encouraged to set this. The protocol field can be in the
form
protocol
:
host
to set both the sending protocol and sending host. For example, “−pU-
UCP:uunet” sets the sending protocol to UUCP and the sending host to uunet. (Some existing
programs use −oM to set the r and s macros; this is equivalent to using −p.)
−q
time
Try to process the queued up mail. If the time is given,
sendmail
will start one or more processes
to run through the queue(s) at the specified time interval to deliver queued mail; otherwise, it only
runs once. Each of these processes acts on a workgroup. These processes are also known as
workgroup processes or WGP’s for short. Each workgroup is responsible for controlling the pro-
cessing of one or more queues; workgroups help manage the use of system resources by sendmail.
Each workgroup may have one or more children concurrently processing queues depending on the
setting of
MaxQueueChildren
.
−qp
time
Similar to −q with a time argument, except that instead of periodically starting WGP’s sendmail
starts persistent WGP’s that alternate between processing queues and sleeping. The sleep time is
specified by the time argument; it defaults to 1 second, except that a WGP always sleeps at least 5
seconds if their queues were empty in the previous run. Persistent processes are managed by a
queue control process (QCP). The QCP is the parent process of the WGP’s. Typically the QCP
will be the sendmail daemon (when started with −bd or −bD) or a special process (named Queue
control) (when started without −bd or −bD). If a persistent WGP ceases to be active for some rea-
son another WGP will be started by the QCP for the same workgroup in most cases. When a per-
sistent WGP has core dumped, the debug flag
no_persistent_restart
is set or the specific persistent
WGP has been restarted too many times already then the WGP will not be started again and a mes-
sage will be logged to this effect. To stop (SIGTERM) or restart (SIGHUP) persistent WGP’s the
appropriate signal should be sent to the QCP. The QCP will propagate the signal to all of the
WGP’s and if appropriate restart the persistent WGP’s.
−q
Gname
Run the jobs in the queue group
name
once.
−q[!]
Xstring
Run the queue once, limiting the jobs to those matching
Xstring
. The key letter
X
can be
I
to limit
based on queue identifier,
R
to limit based on recipient,
S
to limit based on sender, or
Q
to limit
based on quarantine reason for quarantined jobs. A particular queued job is accepted if one of the
corresponding attributes contains the indicated
string
. The optional ! character negates the condi-
tion tested. Multiple
−qX
flags are permitted, with items with the same key letter “or’ed” together,
and items with different key letters “and’ed” together.
−Q[reason] Quarantine normal queue items with the given reason or unquarantine quarantined queue items if
no reason is given. This should only be used with some sort of item matching using
−q[!]
Xstring
as described above.
−R ret
What information you want returned if the message bounces;
ret
can be “HDRS” for headers only
or “FULL” for headers plus body. This is a request only; the other end is not required to honor the
SMM:08-106 Sendmail Installation and Operation Guide
parameter. If “HDRS” is specified local bounces also return only the headers.
−t Read the header for “To:”, “Cc:”, and “Bcc:” lines, and send to everyone listed in those lists. The
“Bcc:” line will be deleted before sending. Any addresses in the argument vector will be deleted
from the send list.
−U This option is required when sending mail using UTF-8; it sets the “SMTPUTF8” argument for
“MAIL” command. Only available if “EAI” support is enabled, and the “SMTPUTF8” option is
set.
−V envid The indicated
envid
is passed with the envelope of the message and returned if the message
bounces.
−X
logfile
Log all traffic in and out of
sendmail
in the indicated
logfile
for debugging mailer problems. This
produces a lot of data very quickly and should be used sparingly.
There are a number of options that may be specified as primitive flags. These are the e, i, m, and v options.
Also, the f option may be specified as the
−s
flag. The DSN related options “−N”, “−R”, and “−V” have no effects
on
sendmail
running as daemon.
Appendix B
QUEUE FILE FORMATS
This appendix describes the format of the queue files. These files live in a queue directory. The individual qf,
hf, Qf, df, and xf files may be stored in separate
qf/
,
df/
, and
xf/
subdirectories if they are present in the queue direc-
tory.
All queue files have the name
ttYMDhmsNNpppppp
where
YMDhmsNNpppppp
is the
id
for this message and
the
tt
is a type. The individual letters in the
id
are:
Y
Encoded year
M
Encoded month
D
Encoded day
h
Encoded hour
m
Encoded minute
s
Encoded second
NN Encoded envelope number
pppppp At least six decimal digits of the process ID
All files with the same id collectively define one message. Due to the use of memory-buffered files, some of
these files may never appear on disk.
The types are:
qf The queue control file. This file contains the information necessary to process the job.
hf The same as a queue control file, but for a quarantined queue job.
df The data file. The message body (excluding the header) is kept in this file. Sometimes the df file is not
stored in the same directory as the qf file; in this case, the qf file contains a ‘d’ record which names the
queue directory that contains the df file.
tf A temporary file. This is an image of the
qf
file when it is being rebuilt. It should be renamed to a
qf
file
very quickly.
xf A transcript file, existing during the life of a session showing everything that happens during that session.
Sometimes the xf file must be generated before a queue group has been selected; in this case, the xf file will
be stored in a directory of the default queue group.
Qf A ‘‘lost’’ queue control file.
sendmail
renames a
qf
file to
Qf
if there is a severe (configuration) problem
that cannot be solved without human intervention. Search the logfile for the queue file id to figure out what
happened. After you resolved the problem, you can rename the
Qf
file to
qf
and send it again.
The queue control file is structured as a series of lines each beginning with a code letter; the file must end with
a line containing only a single dot. The lines are as follows:
V
The version number of the queue file format, used to allow new
sendmail
binaries to read queue files cre-
ated by older versions. Defaults to version zero. Must be the first line of the file if present. For 8.13 and
later the version number is 8.
A
The information given by the AUTH= parameter of the
SMTP MAIL
command or $f@$j if sendmail has
been called directly.
Sendmail Installation and Operation Guide
SMM:08-107
SMM:08-108 Sendmail Installation and Operation Guide
H
A header definition. There may be any number of these lines. The order is important: they represent the
order in the final message. These use the same syntax as header definitions in the configuration file.
C
The controlling address. The syntax is “localuser:aliasname”. Recipient addresses following this line will
be flagged so that deliveries will be run as the
localuser
(a user name from the /etc/passwd file);
aliasname
is the name of the alias that expanded to this address (used for printing messages).
q
The quarantine reason for quarantined queue items.
Q
The ‘‘original recipient’’, specified by the ORCPT= field in an ESMTP transaction. Used exclusively for
Delivery Status Notifications. It applies only to the following ‘R’ line.
r
The ‘‘final recipient’’ used for Delivery Status Notifications. It applies only to the following ‘R’ line.
R
A recipient address. This will normally be completely aliased, but is actually realiased when the job is
processed. There will be one line for each recipient, which also includes a leading colon-terminated list of
flags, some of which are ‘S’ to return a message on successful final delivery, ‘F’ to return a message on fail-
ure, ‘D’ to return a message if the message is delayed, ‘N’ to suppress returning the body, ‘A’ to indicate
this is an expanded alias, ‘X’ to declare that MX lookups were secure (DNSSEC), and ‘P’ to declare this as
a ‘‘primary’’ (command line or SMTP-session) address.
S
The sender address. There may only be one of these lines.
T
The job creation time. This is used to compute when to time out the job.
P
The current message priority. This is used to order the queue. Higher numbers mean lower priorities. The
priority changes as the message sits in the queue. The initial priority depends on the message class and the
size of the message.
M
A message. This line is printed by the
mailq
command, and is generally used to store status information. It
can contain any text.
F
Flag bits, represented as one letter per flag. Defined flag bits are
r
indicating that this is a response message
and
w
indicating that a warning message has been sent announcing that the mail has been delayed. Other
flag bits are:
8
: the body contains 8bit data,
b
: a Bcc: header should be removed,
d
: the mail has RET para-
meters (see RFC 1894),
n
: the body of the message should not be returned in case of an error,
s
: the enve-
lope has been split.
N
The total number of delivery attempts.
K
The time (as seconds since January 1, 1970) of the last delivery attempt.
d
If the df file is in a different directory than the qf file, then a ‘d’ record is present, specifying the directory in
which the df file resides.
I
The i-number of the data file; this can be used to recover your mail queue after a disastrous disk crash.
$
A macro definition. The values of certain macros are passed through to the queue run phase.
B
The body type. The remainder of the line is a text string defining the body type. If this field is missing, the
body type is assumed to be “undefined” and no special processing is attempted. Legal values are “7BIT”
and “8BITMIME”.
Z
The original envelope id (from the ESMTP transaction). For Deliver Status Notifications only.
!
Information for Deliver-By SMTP extension.
As an example, the following is a queue file sent to “eric@mammoth.Berkeley.EDU” and “bostic@oke-
effe.CS.Berkeley.EDU”
1
:
1
This example is contrived and probably inaccurate for your environment. Glance over it to get an idea; nothing can replace looking at
what your own system generates.
Sendmail Installation and Operation Guide
SMM:08-109
V4
T711358135
K904446490
N0
P2100941
$_eric@localhost
${daemon_flags}
Seric
Ceric:100:1000:sendmail@vangogh.CS.Berkeley.EDU
RPFD:eric@mammoth.Berkeley.EDU
RPFD:bostic@okeeffe.CS.Berkeley.EDU
H?P?Return-path: <ˆg>
H??Received: by vangogh.CS.Berkeley.EDU (5.108/2.7) id AAA06703;
Fri, 17 Jul 1992 00:28:55 -0700
H??Received: from mail.CS.Berkeley.EDU by vangogh.CS.Berkeley.EDU (5.108/2.7)
id AAA06698; Fri, 17 Jul 1992 00:28:54 -0700
H??Received: from [128.32.31.21] by mail.CS.Berkeley.EDU (5.96/2.5)
id AA22777; Fri, 17 Jul 1992 03:29:14 -0400
H??Received: by foo.bar.baz.de (5.57/Ultrix3.0-C)
id AA22757; Fri, 17 Jul 1992 09:31:25 GMT
H?F?From: eric@foo.bar.baz.de (Eric Allman)
H?x?Full-name: Eric Allman
H??Message-id: <9207170931.AA22757@foo.bar.baz.de>
H??To: sendmail@vangogh.CS.Berkeley.EDU
H??Subject: this is an example message
.
This shows the person who sent the message, the submission time (in seconds since January 1, 1970), the message
priority, the message class, the recipients, and the headers for the message.
Appendix C
SUMMARY OF SUPPORT FILES
This is a summary of the support files that
sendmail
creates or generates. Many of these can be changed by
editing the sendmail.cf file; check there to find the actual pathnames.
/usr/sbin/sendmail
The binary of
sendmail
.
/usr/bin/newaliases
A link to /usr/sbin/sendmail; causes the alias database to be rebuilt. Running this program is com-
pletely equivalent to giving
sendmail
the
−bi
flag.
/usr/bin/mailq Prints a listing of the mail queue. This program is equivalent to using the
−bp
flag to
sendmail
.
/etc/mail/sendmail.cf
The configuration file, in textual form.
/etc/mail/helpfile The SMTP help file.
/etc/mail/statistics
A statistics file; need not be present.
/etc/mail/sendmail.pid
Created in daemon mode; it contains the process id of the current SMTP daemon. If you use this
in scripts; use ‘‘head −1’’ to get just the first line; the second line contains the command line used
to invoke the daemon, and later versions of
sendmail
may add more information to subsequent
lines.
/etc/mail/aliases The textual version of the alias file.
/etc/mail/aliases.db
The alias file in
hash
(3) format.
/etc/mail/aliases.{pag,dir}
The alias file in
ndbm
(3) format.
/var/spool/mqueue
The directory in which the mail queue(s) and temporary files reside.
/var/spool/mqueue/qf*
Control (queue) files for messages.
/var/spool/mqueue/df*
Data files.
/var/spool/mqueue/tf*
Temporary versions of the qf files, used during queue file rebuild.
/var/spool/mqueue/xf*
A transcript of the current session.
SMM:08-110 Sendmail Installation and Operation Guide
Sendmail Installation and Operation Guide
SMM:08-3
TABLE OF CONTENTS
1. BASIC INSTALLATION .............................................................................................................................
7
1.1. Compiling Sendmail ............................................................................................................................
7
1.1.1. Tweaking the Build Invocation ...................................................................................................
7
1.1.2. Creating a Site Configuration File .............................................................................................. 7
1.1.3. Tweaking the Makefile ................................................................................................................
7
1.1.4. Compilation and installation ....................................................................................................... 8
1.2. Configuration Files ..............................................................................................................................
8
1.3. Details of Installation Files .................................................................................................................. 9
1.3.1. /usr/sbin/sendmail ....................................................................................................................... 9
1.3.2. /etc/mail/sendmail.cf ................................................................................................................... 10
1.3.3. /etc/mail/submit.cf ...................................................................................................................... 10
1.3.4. /usr/bin/newaliases ......................................................................................................................
10
1.3.5. /usr/bin/hoststat ........................................................................................................................... 10
1.3.6. /usr/bin/purgestat ........................................................................................................................
10
1.3.7. /var/spool/mqueue .......................................................................................................................
10
1.3.8. /var/spool/clientmqueue ..............................................................................................................
11
1.3.9. /var/spool/mqueue/.hoststat ........................................................................................................
11
1.3.10. /etc/mail/aliases* ....................................................................................................................... 11
1.3.11. /etc/rc or /etc/init.d/sendmail .................................................................................................... 11
1.3.12. /etc/mail/helpfile ....................................................................................................................... 12
1.3.13. /etc/mail/statistics ..................................................................................................................... 12
1.3.14. /usr/bin/mailq ............................................................................................................................ 12
1.3.15. sendmail.pid .............................................................................................................................. 12
1.3.16. Map Files ..................................................................................................................................
14
2. NORMAL OPERATIONS ............................................................................................................................
14
2.1. The System Log ................................................................................................................................... 14
2.1.1. Format .........................................................................................................................................
14
2.1.2. Levels ..........................................................................................................................................
15
2.2. Dumping State .....................................................................................................................................
15
2.3. The Mail Queues .................................................................................................................................. 15
2.3.1. Queue Groups and Queue Directories ........................................................................................ 15
2.3.2. Queue Runs .................................................................................................................................
16
2.3.3. Manual Intervention ....................................................................................................................
16
2.3.4. Printing the queue ....................................................................................................................... 16
2.3.5. Forcing the queue ....................................................................................................................... 17
2.3.6. Quarantined Queue Items ........................................................................................................... 17
2.4. Disk Based Connection Information ................................................................................................... 18
2.5. The Service Switch .............................................................................................................................. 18
2.6. The Alias Database .............................................................................................................................. 19
2.6.1. Rebuilding the alias database ...................................................................................................... 20
2.6.2. Potential problems ......................................................................................................................
20
2.6.3. List owners ..................................................................................................................................
21
SMM:08-4 Sendmail Installation and Operation Guide
2.7. User Information Database .................................................................................................................. 21
2.8. Per-User Forwarding (.forward Files) .................................................................................................. 21
2.9. Special Header Lines ........................................................................................................................... 21
2.9.1. Errors-To: ....................................................................................................................................
21
2.9.2. Apparently-To: ............................................................................................................................
22
2.9.3. Precedence .................................................................................................................................. 22
2.10. IDENT Protocol Support ................................................................................................................... 22
3. ARGUMENTS ............................................................................................................................................. 22
3.1. Queue Interval ......................................................................................................................................
23
3.2. Daemon Mode .....................................................................................................................................
23
3.3. Forcing the Queue ................................................................................................................................ 23
3.4. Debugging ............................................................................................................................................
23
3.5. Changing the Values of Options .......................................................................................................... 24
3.6. Trying a Different Configuration File .................................................................................................. 24
3.7. Logging Traffic ....................................................................................................................................
24
3.8. Testing Configuration Files .................................................................................................................. 25
3.9. Persistent Host Status Information ...................................................................................................... 26
4. TUNING ....................................................................................................................................................... 26
4.1. Timeouts ..............................................................................................................................................
26
4.1.1. Queue interval .............................................................................................................................
26
4.1.2. Read timeouts .............................................................................................................................
27
4.1.3. Message timeouts ........................................................................................................................
28
4.2. Forking During Queue Runs ................................................................................................................ 29
4.3. Queue Priorities ...................................................................................................................................
29
4.4. Load Limiting ......................................................................................................................................
29
4.5. Resource Limits ...................................................................................................................................
30
4.6. Measures against Denial of Service Attacks ....................................................................................... 30
4.7. Delivery Mode ..................................................................................................................................... 30
4.8. Log Level ............................................................................................................................................. 31
4.9. File Modes ...........................................................................................................................................
31
4.9.1. To suid or not to suid? ................................................................................................................ 31
4.9.2. Turning off security checks ........................................................................................................ 32
4.10. Connection Caching ...........................................................................................................................
34
4.11. Name Server Access .......................................................................................................................... 34
4.12. Moving the Per-User Forward Files .................................................................................................. 35
4.13. Free Space ..........................................................................................................................................
36
4.14. Maximum Message Size .................................................................................................................... 36
4.15. Privacy Flags ......................................................................................................................................
36
4.16. Send to Me Too ..................................................................................................................................
36
5. THE WHOLE SCOOP ON THE CONFIGURATION FILE ....................................................................... 36
5.1. R and S — Rewriting Rules ................................................................................................................. 37
5.1.1. The left hand side ........................................................................................................................ 37
5.1.2. The right hand side ..................................................................................................................... 37
5.1.3. Semantics of rewriting rule sets .................................................................................................. 39
Sendmail Installation and Operation Guide
SMM:08-5
5.1.4. Ruleset hooks ..............................................................................................................................
40
5.1.4.1. check_relay ........................................................................................................................ 40
5.1.4.2. check_mail ......................................................................................................................... 40
5.1.4.3. check_rcpt .......................................................................................................................... 40
5.1.4.4. check_data ......................................................................................................................... 40
5.1.4.5. check_other ........................................................................................................................ 40
5.1.4.6. check_compat .................................................................................................................... 41
5.1.4.7. check_eoh .......................................................................................................................... 41
5.1.4.8. check_eom ......................................................................................................................... 42
5.1.4.9. check_etrn .......................................................................................................................... 42
5.1.4.10. check_expn ......................................................................................................................
42
5.1.4.11. check_vrfy ....................................................................................................................... 42
5.1.4.12. clt_features ....................................................................................................................... 42
5.1.4.13. trust_auth ......................................................................................................................... 43
5.1.4.14. tls_client ........................................................................................................................... 43
5.1.4.15. tls_server ..........................................................................................................................
43
5.1.4.16. tls_rcpt ............................................................................................................................. 43
5.1.4.17. srv_features ...................................................................................................................... 43
5.1.4.18. try_tls ............................................................................................................................... 45
5.1.4.19. tls_srv_features and tls_clt_features ................................................................................ 45
5.1.4.20. authinfo ............................................................................................................................ 46
5.1.4.21. queuegroup ......................................................................................................................
46
5.1.4.22. greet_pause ...................................................................................................................... 46
5.1.5. IPC mailers .................................................................................................................................
46
5.2. D — Define Macro .............................................................................................................................. 47
5.3. C and F — Define Classes ................................................................................................................... 54
5.4. E — Set or Propagate Environment Variables .....................................................................................
55
5.5. M — Define Mailer ............................................................................................................................. 56
5.6. H — Define Header ............................................................................................................................. 60
5.7. O — Set Option ................................................................................................................................... 61
5.8. P — Precedence Definitions ................................................................................................................ 79
5.9. V — Configuration Version Level ....................................................................................................... 79
5.10. K — Key File Declaration ................................................................................................................. 80
5.11. Q — Queue Group Declaration ......................................................................................................... 88
5.12. X — Mail Filter (Milter) Definitions ................................................................................................. 89
5.13. The User Database ............................................................................................................................. 90
5.13.1. Structure of the user database ................................................................................................... 90
5.13.2. User database semantics ........................................................................................................... 91
5.13.3. Creating the database
23
............................................................................................................. 91
6. OTHER CONFIGURATION ........................................................................................................................
92
6.1. Parameters in devtools/OS/$oscf .........................................................................................................
92
6.1.1. For Future Releases .................................................................................................................... 93
6.2. Parameters in sendmail/conf.h ............................................................................................................. 93
6.3. Configuration in sendmail/conf.c ......................................................................................................... 95
SMM:08-6 Sendmail Installation and Operation Guide
6.3.1. Built-in Header Semantics .......................................................................................................... 95
6.3.2. Restricting Use of Email ............................................................................................................. 97
6.3.3. New Database Map Classes ........................................................................................................ 97
6.3.4. Queueing Function ......................................................................................................................
98
6.3.5. Refusing Incoming SMTP Connections ..................................................................................... 98
6.3.6. Load Av erage Computation ........................................................................................................ 98
6.4. Configuration in sendmail/daemon.c ................................................................................................... 99
6.5. LDAP ...................................................................................................................................................
99
6.5.1. LDAP Recursion ......................................................................................................................... 99
6.5.1.1. Example ............................................................................................................................. 99
6.6. STARTTLS ..........................................................................................................................................
100
6.6.1. Certificates for STARTTLS ........................................................................................................
100
6.6.2. PRNG for STARTTLS ................................................................................................................
101
6.7. Encoding of STARTTLS and AUTH related Macros .......................................................................... 101
6.8. DANE ..................................................................................................................................................
101
6.9. EAI ....................................................................................................................................................... 102
6.10. MTA-STS ...........................................................................................................................................
102
7. ACKNOWLEDGEMENTS ..........................................................................................................................
102
Appendix A. COMMAND LINE FLAGS ........................................................................................................
104
Appendix B. QUEUE FILE FORMATS ..........................................................................................................
107
Appendix C. SUMMARY OF SUPPORT FILES ............................................................................................
110