Postfix Installation From Source Code


1 - Purpose of this document

If you are using a pre-compiled version of Postfix, you should start with BASIC_CONFIGURATION_README and the general documentation referenced by it. INSTALL is only a bootstrap document to get Postfix up and running from scratch with the minimal number of steps; it should not be considered part of the general documentation.

This document describes how to build, install and configure a Postfix system so that it can do one of the following:

Topics covered in this document:

  1. Purpose of this document
  2. Typographical conventions
  3. Documentation
  4. Building on a supported system
  5. Porting Postfix to an unsupported system
  6. Installing the software after successful compilation
  7. Configuring Postfix to send mail only
  8. Configuring Postfix to send and receive mail via virtual interface
  9. Running Postfix instead of Sendmail
  10. Mandatory configuration file edits
  11. To chroot or not to chroot
  12. Care and feeding of the Postfix system

2 - Typographical conventions

In the instructions below, a command written as

# command

should be executed as the superuser.

A command written as

$ command

should be executed as an unprivileged user.

3 - Documentation

Documentation is available as README files (start with the file README_FILES/AAAREADME), as HTML web pages (point your browser to "html/index.html") and as UNIX-style manual pages.

You should view the README files with a pager such as more(1) or less(1), because the files use backspace characters in order to produce bold font. To print a README file without backspace characters, use the col(1) command. For example:

$ col -bx <file | lpr

In order to view the manual pages before installing Postfix, point your MANPATH environment variable to the "man" subdirectory; be sure to use an absolute path.

$ export MANPATH; MANPATH="`pwd`/man:$MANPATH"
$ setenv MANPATH "`pwd`/man:$MANPATH"

Of particular interest is the postconf(5) manual page that lists all the 500+ configuration parameters. The HTML version of this text makes it easy to navigate around.

All Postfix source files have their own built-in manual page. Tools to extract those embedded manual pages are available in the mantools directory.

4 - Building on a supported system

At some point in time, a version of Postfix was supported on:

AIX 3.2.5, 4.1.x, 4.2.0, 4.3.x, 5.2
BSD/OS 2.x, 3.x, 4.x
FreeBSD 2.x .. 9.x
HP-UX 9.x, 10.x, 11.x
IRIX 5.x, 6.x
Linux Debian 1.3.1 and later
Linux RedHat 3.x (January 2004) and later
Linux Slackware 3.x and later
Linux SuSE 5.x and later
Linux Ubuntu 4.10 and later
Mac OS X
NEXTSTEP 3.x
NetBSD 1.x and later
OPENSTEP 4.x
OSF1.V3 - OSF1.V5 (Digital UNIX)
Reliant UNIX 5.x
SunOS 4.1.4 (March 2007)
SunOS 5.4 - 5.10 (Solaris 2.4..10)
Ultrix 4.x (well, that was long ago)

or something closely resemblant.

4.1 - Getting started

On Solaris, the "make" command and other utilities for software development are in /usr/ccs/bin, so you MUST have /usr/ccs/bin in your command search path. If these files do not exist, install the development packages first. See the Solaris FAQ item "Which packages do I need to install to support a C compiler?".

If you need to build Postfix for multiple architectures, use the "lndir" command to build a shadow tree with symbolic links to the source files. "lndir" is part of X11R6.

If at any time in the build process you get messages like: "make: don't know how to ..." you should be able to recover by running the following command from the Postfix top-level directory:

$ make -f Makefile.init makefiles

If you copied the Postfix source code after building it on another machine, it is a good idea to cd into the top-level directory and first do this:

$ make tidy

This will get rid of any system dependencies left over from compiling the software elsewhere.

4.2 - What compiler to use

To build with GCC, or with the native compiler if people told me that is better for your system, just cd into the top-level Postfix directory of the source tree and type:

$ make

To build with a non-default compiler, you need to specify the name of the compiler. Here are a few examples:

$ make makefiles CC=/opt/SUNWspro/bin/cc        (Solaris)
$ make

$ make makefiles CC="/opt/ansic/bin/cc -Ae"     (HP-UX)
$ make

$ make makefiles CC="purify cc"
$ make

and so on. In some cases, optimization is turned off automatically.

4.3 - Building with Postfix shared libraries and database plugins (Postfix ≥ 2.12)

Postfix shared-library and database plugin support exists for recent versions of Linux, FreeBSD and MacOS X. Shared-library builds may become the default at some point in the future.

Overview of topics:

Note: directories with Postfix shared libraries or database plugins should contain only postfix-related files. Postfix shared libraries and database plugins should not be installed in a "public" system directory such as /usr/lib or /usr/local/lib. Linking Postfix shared-library or database-plugin files into non-Postfix programs is not supported. Postfix shared libraries and database plugins implement a Postfix-internal API that changes without maintaining compatibility.

4.3.1 Turning on Postfix shared-library support

Postfix can be built with Postfix shared libraries (files typically named libpostfix-*.so). Postfix shared libraries add minor run-time overhead and result in significantly-smaller Postfix executable files.

Specify "shared=yes" on the "make makefiles" command line to build Postfix with shared-library support.

$ make makefiles shared=yes ...other arguments...
$ make

(Specify "make makefiles shared=no" to explicitly disable Postfix shared-library support).

This installs shared libraries in $shlib_directory, typically /usr/lib/postfix or /usr/local/lib/postfix, with file names libpostfix-name.so, where the name is a source-code directory name such as "util" or "global".

See section 4.3.3 "Customizing Postfix shared libraries and database plugins" below for how to customize the Postfix shared-library location, including support to upgrade a running mail system safely.

4.3.2 Turning on Postfix database-plugin support

Additionally, Postfix can be built to support dynamic loading of Postfix database clients (database plugins) with the Debian-style dynamicmaps feature. Postfix 2.12 supports dynamic loading of cdb:, ldap:, lmdb:, mysql:, pcre:, pgsql:, sdbm:, and sqlite: database clients. Dynamic loading is useful when you distribute or install pre-compiled Postfix packages.

Specify "dynamicmaps=yes" on the "make makefiles" command line to build Postfix with support to dynamically load Postfix database clients with the Debian-style dynamicmaps feature.

$ make makefiles dynamicmaps=yes ...other arguments...
$ make

(Specify "make makefiles dynamicmaps=no" to explicitly disable Postfix database-plugin support).

This implicitly enables shared-library support, installs the configuration file dynamicmaps.cf in $meta_directory (usually, /etc/postfix or /usr/local/etc/postfix), and installs database plugins in $shlib_directory (see above). Database plugins are named postfix-type.so where the type is a database type such as "cdb" or "ldap".

NOTE: The Postfix 2.12 build procedure expects that you specify database library dependencies with variables named AUXLIBS_CDB, AUXLIBS_LDAP, etc. With Postfix 2.12 and later, the old AUXLIBS variable still supports building a statically-loaded database client, but only the new AUXLIBS_CDB etc. variables support building a dynamically-loaded or statically-loaded CDB etc. database client. See CDB_README, LDAP_README, etc. for details.

Failure to follow this advice will defeat the purpose of dynamic database client loading. Every Postfix executable file will have database library dependencies. And that was exactly what dynamic database client loading was meant to avoid.

See the next section for how to customize the location and version of Postfix database plugins and the location of the file dynamicmaps.cf.

4.3.3 Customizing Postfix shared libraries and database plugins

Customizing the location of Postfix shared libraries and database plugins

As a reminder, the directories with Postfix shared libraries or database plugins should contain only Postfix-related files. Linking these files into other programs is not supported.

To override the default location of Postfix shared libraries and database plugins specify, for example:

$ make makefiles shared=yes shlib_directory=/usr/local/lib/postfix ...

If you intend to upgrade Postfix without stopping the mail system, then you should append the Postfix release version to the shlib_directory pathname, to eliminate the possibility that programs will link with shared libraries or database plugins from the wrong Postfix version. For example:

$ make makefiles shared=yes \
    shlib_directory=/usr/local/lib/postfix/MAIL_VERSION ...

The command "make makefiles name=value..." will replace the string MAIL_VERSION at the end of a configuration parameter value with the Postfix release version. Do not try to specify something like $mail_version on this command line. This produces inconsistent results with different versions of the make(1) command.

You can change the shlib_directory setting after Postfix is built, with "make install" or "make upgrade". However, you may have to run ldconfig if you change shlib_directory after Postfix is built (the symptom is that Postfix programs fail because the run-time linker cannot find the files libpostfix-*.so). No ldconfig command is needed if you keep the files libpostfix-*.so in the compiled-in default $shlib_directory location.

# make upgrade shlib_directory=/usr/local/lib/postfix ...
# make install shlib_directory=/usr/local/lib/postfix ...

To append the Postfix release version to the pathname if you intend to upgrade Postfix without stopping the mail system:

# make upgrade shlib_directory=/usr/local/lib/postfix/MAIL_VERSION ...
# make install shlib_directory=/usr/local/lib/postfix/MAIL_VERSION ...

See also the comments above for appending MAIL_VERSION with the "make makefiles" command.

Customizing the location of dynamicmaps.cf and other files

The meta_directory parameter has the same default setting as the config_directory parameter, typically /etc/postfix or /usr/local/etc/postfix.

You can override the default meta_directory location at compile time or after Postfix is built. To override the default location at compile time specify, for example:

% make makefiles meta_directory=/usr/libexec/postfix ...

Here is a tip if you want to make a pathname dependent on the Postfix release version: the command "make makefiles name=value..." will replace the string MAIL_VERSION at the end of a configuration parameter value with the Postfix release version. Do not try to specify something like $mail_version on this command line. This produces inconsistent results with different versions of the make(1) command.

You can override the meta_directory setting after Postfix is built, with "make install" or "make upgrade".

# make upgrade meta_directory=/usr/libexec/postfix ...
# make install meta_directory=/usr/libexec/postfix ...

As with the command "make makefiles, the command "make install/upgrade name=value..." will replace the string MAIL_VERSION at the end of a configuration parameter value with the Postfix release version. Do not try to specify something like $mail_version on this command line. This produces inconsistent results with different versions of the make(1) command.

4.4.4 Tips for distribution maintainers

4.4 - Building with optional features

By default, Postfix builds as a mail system with relatively few bells and whistles. Support for third-party databases etc. must be configured when Postfix is compiled. The following documents describe how to build Postfix with support for optional features:
Optional feature Document Availability
Berkeley DB database DB_README Postfix 1.0
LMDB database LMDB_README Postfix 2.11
LDAP database LDAP_README Postfix 1.0
MySQL database MYSQL_README Postfix 1.0
Perl compatible regular expression PCRE_README Postfix 1.0
PostgreSQL database PGSQL_README Postfix 2.0
SASL authentication SASL_README Postfix 1.0
SQLite database SQLITE_README Postfix 2.8
STARTTLS session encryption TLS_README Postfix 2.2

Note: IP version 6 support is compiled into Postfix on operating systems that have IPv6 support. See the IPV6_README file for details.

4.5 - Overriding built-in parameter default settings

4.5.1 - Postfix 2.12 and later

All Postfix configuration parameters can be changed by editing a Postfix configuration file, except for one: the parameter that specifies the location of Postfix configuration files. In order to build Postfix with a configuration directory other than /etc/postfix, use:

$ make makefiles config_directory=/some/where ...other arguments...
$ make

The command "make makefiles name=value ..." will replace the string MAIL_VERSION at the end of a configuration parameter value with the Postfix release version. Do not try to specify something like $mail_version on this command line. This produces inconsistent results with different versions of the make(1) command.

Parameters whose defaults can be specified in this way are listed below. See the postconf(5) manpage for a description (command: "nroff -man man/man5/postconf.5 | less").

parameter name typical default
command_directory /usr/sbin
config_directory /etc/postfix
default_database_type hash
daemon_directory /usr/libexec/postfix
data_directory /var/lib/postfix
html_directory no
mail_spool_directory /var/mail
mailq_path /usr/bin/mailq
manpage_directory /usr/local/man
meta_directory /etc/postfix
newaliases_path /usr/bin/newaliases
queue_directory /var/spool/postfix
readme_directory no
sendmail_path /usr/sbin/sendmail
shlib_directory /usr/lib/postfix

4.5.2 - All Postfix versions

All Postfix configuration parameters can be changed by editing a Postfix configuration file, except for one: the parameter that specifies the location of Postfix configuration files. In order to build Postfix with a configuration directory other than /etc/postfix, use:

$ make makefiles CCARGS='-DDEF_CONFIG_DIR=\"/some/where\"'
$ make

IMPORTANT: Be sure to get the quotes right. These details matter a lot.

Parameters whose defaults can be specified in this way are listed below. See the postconf(5) manpage for a description (command: "nroff -man man/man5/postconf.5 | less").

Macro name default value for typical default
DEF_COMMAND_DIR command_directory /usr/sbin
DEF_CONFIG_DIR config_directory /etc/postfix
DEF_DB_TYPE default_database_type hash
DEF_DAEMON_DIR daemon_directory /usr/libexec/postfix
DEF_DATA_DIR data_directory /var/lib/postfix
DEF_MAILQ_PATH mailq_path /usr/bin/mailq
DEF_HTML_DIR html_directory no
DEF_MANPAGE_DIR manpage_directory /usr/local/man
DEF_NEWALIAS_PATH newaliases_path /usr/bin/newaliases
DEF_QUEUE_DIR queue_directory /var/spool/postfix
DEF_README_DIR readme_directory no
DEF_SENDMAIL_PATH sendmail_path /usr/sbin/sendmail

Note: the data_directory parameter (for caches and pseudo-random numbers) was introduced with Postfix version 2.5.

4.6 - Overriding other compile-time features

The general method to override Postfix compile-time features is as follows:

$ make makefiles name=value name=value...
$ make

The following is an extensive list of names and values.

Name/Value Description
AUXLIBS="object_library..." Specifies one or more non-default object libraries. Postfix 2.12 and later specify some of their database library dependencies with AUXLIBS_CDB, AUXLIBS_LDAP, AUXLIBS_LMDB, AUXLIBS_MYSQL, AUXLIBS_PCRE, AUXLIBS_PGSQL, AUXLIBS_SDBM, and AUXLIBS_SQLITE, respectively.
CC=compiler_command Specifies a non-default compiler. On many systems, the default is gcc.
CCARGS="compiler_arguments..." Specifies non-default compiler arguments, for example, a non-default include directory. The following directives turn off Postfix features at compile time:
-DNO_DB Do not build with Berkeley DB support. By default, Berkeley DB support is compiled in on platforms that are known to support this feature. If you override this, then you probably should also override DEF_DB_TYPE as described in section 4.5.
-DNO_DEVPOLL Do not build with Solaris /dev/poll support. By default, /dev/poll support is compiled in on Solaris versions that are known to support this feature.
-DNO_EPOLL Do not build with Linux EPOLL support. By default, EPOLL support is compiled in on platforms that are known to support this feature.
-DNO_EAI Do not build with EAI (SMTPUTF8) support. By default, EAI support is compiled in when the "icuuc" library and header files are found.
-DNO_IPV6 Do not build with IPv6 support. By default, IPv6 support is compiled in on platforms that are known to have IPv6 support. Note: this directive is for debugging and testing only. It is not guaranteed to work on all platforms.
-DNO_KQUEUE Do not build with FreeBSD / NetBSD / OpenBSD / MacOSX KQUEUE support. By default, KQUEUE support is compiled in on platforms that are known to support it.
-DNO_NIS Do not build with NIS or NISPLUS support. NIS is not available on some recent Linux distributions.
-DNO_NISPLUS Do not build with NISPLUS support. NISPLUS is not available on some recent Solaris distributions.
-DNO_PCRE Do not build with PCRE support. By default, PCRE support is compiled in when the pcre-config utility is installed.
-DNO_POSIX_GETPW_R Disable support for POSIX getpwnam_r/getpwuid_r. By default Postfix uses these where they are known to be available.
-DNO_SIGSETJMP Use setjmp()/longjmp() instead of sigsetjmp()/siglongjmp(). By default, Postfix uses sigsetjmp()/siglongjmp() when they are known to be available.
DEBUG=debug_level Specifies a non-default compiler debugging level. The default is -g. Specify DEBUG= to turn off debugging.
OPT=optimization_level Specifies a non-default optimization level. The default is -O. Specify OPT= to turn off optimization.
WARN="warning_flags..." Specifies non-default gcc compiler warning options for use when "make" is invoked in a source subdirectory only.

4.7 - Support for thousands of processes

The number of connections that Postfix can manage simultaneously is limited by the number of processes that it can run. This number in turn is limited by the number of files and sockets that a single process can open. For example, the Postfix queue manager has a separate connection to each delivery process, and the anvil(8) server has one connection per smtpd(8) process.

Postfix version 2.4 and later have no built-in limits on the number of open files or sockets, when compiled on systems that support one of the following:

With other Postfix versions or operating systems, the number of file descriptors per process is limited by the value of the FD_SETSIZE macro. If you expect to run more than 1000 mail delivery processes, you may need to override the definition of the FD_SETSIZE macro to make select() work correctly:

$ make makefiles CCARGS=-DFD_SETSIZE=2048

Warning: the above has no effect on some Linux versions. Apparently, on these systems the FD_SETSIZE value can be changed only by using undocumented interfaces. Currently, that means including <bits/types.h> directly (which is not allowed) and overriding the __FD_SETSIZE macro. Beware, undocumented interfaces can change at any time and without warning.

But wait, there is more: none of this will work unless the operating system is configured to handle thousands of connections. See the TUNING_README guide for examples of how to increase the number of open sockets or files.

4.8 - Compiling Postfix, at last

If the command

$ make

is successful, then you can proceed to install Postfix (section 6).

If the command produces compiler error messages, it may be time to search the web or to ask the postfix-users@postfix.org mailing list, but be sure to search the mailing list archives first. Some mailing list archives are linked from http://www.postfix.org/.

5 - Porting Postfix to an unsupported system

Each system type that Postfix knows is identified by a unique name. Examples: SUNOS5, FREEBSD4, and so on. When porting Postfix to a new system, the first step is to choose a SYSTEMTYPE name for the new system. You must use a name that includes at least the major version of the operating system (such as SUNOS4 or LINUX2), so that different releases of the same system can be supported without confusion.

Add a case statement to the "makedefs" shell script in the source code top-level directory that recognizes the new system reliably, and that emits the right system-specific information. Be sure to make the code robust against user PATH settings; if the system offers multiple UNIX flavors (e.g. BSD and SYSV) be sure to build for the native flavor, instead of the emulated one.

Add an "#ifdef SYSTEMTYPE" section to the central util/sys_defs.h include file. You may have to invent new feature macro names. Please choose sensible feature macro names such as HAS_DBM or FIONREAD_IN_SYS_FILIO_H.

I strongly recommend against using "#ifdef SYSTEMTYPE" in individual source files. While this may look like the quickest solution, it will create a mess when newer versions of the same SYSTEMTYPE need to be supported. You're likely to end up placing "#ifdef" sections all over the source code again.

6 - Installing the software after successful compilation

This text describes how to install Postfix from source code. See the PACKAGE_README file if you are building a package for distribution to other systems.

6.1 - Save existing Sendmail binaries

IMPORTANT: if you are REPLACING an existing Sendmail installation with Postfix, you may need to keep the old sendmail program running for some time in order to flush the mail queue.

6.2 - Create account and groups

Before you install Postfix for the first time you need to create an account and a group:

6.3 - Install Postfix

To install or upgrade Postfix from compiled source code, run one of the following commands as the super-user:

# make install       (interactive version, first time install)

# make upgrade       (non-interactive version, for upgrades)

6.4 - Configure Postfix

Proceed to the section on how you wish to run Postfix on your particular machine:

7 - Configuring Postfix to send mail only

If you are going to use Postfix to send mail only, there is no need to change your existing sendmail setup. Instead, set up your mail user agent so that it calls the Postfix sendmail program directly.

Follow the instructions in the "Mandatory configuration file edits" in section 10, and review the "To chroot or not to chroot" text in section 11.

You MUST comment out the "smtp inet" entry in /etc/postfix/master.cf, in order to avoid conflicts with the real sendmail. Put a "#" character in front of the line that defines the smtpd service:

/etc/postfix/master.cf:
    #smtp      inet  n       -       n       -       -       smtpd

Start the Postfix system:

# postfix start

or, if you feel nostalgic, use the Postfix sendmail command:

# sendmail -bd -qwhatever

and watch your maillog file for any error messages. The pathname is /var/log/maillog, /var/log/mail, /var/log/syslog, or something else. Typically, the pathname is defined in the /etc/syslog.conf file.

$ egrep '(reject|warning|error|fatal|panic):' /some/log/file

Note: the most important error message is logged first. Later messages are not as useful.

In order to inspect the mail queue, use one of the following commands:

$ mailq

$ sendmail -bp

$ postqueue -p

See also the "Care and feeding" section 12 below.

8 - Configuring Postfix to send and receive mail via virtual interface

Alternatively, you can use the Postfix system to send AND receive mail while leaving your Sendmail setup intact, by running Postfix on a virtual interface address. Simply configure your mail user agent to directly invoke the Postfix sendmail program.

To create a virtual network interface address, study your system ifconfig manual page. The command syntax could be any of:

# ifconfig le0:1 <address> netmask <mask> up
# ifconfig en0 alias <address> netmask 255.255.255.255

In the /etc/postfix/main.cf file, I would specify

/etc/postfix/main.cf:
    myhostname = virtual.host.tld
    inet_interfaces = $myhostname
    mydestination = $myhostname

Follow the instructions in the "Mandatory configuration file edits" in section 10, and review the "To chroot or not to chroot" text in section 11.

Start the Postfix system:

# postfix start

or, if you feel nostalgic, use the Postfix sendmail command:

# sendmail -bd -qwhatever

and watch your maillog file for any error messages. The pathname is /var/log/maillog, /var/log/mail, /var/log/syslog, or something else. Typically, the pathname is defined in the /etc/syslog.conf file.

$ egrep '(reject|warning|error|fatal|panic):' /some/log/file

Note: the most important error message is logged first. Later messages are not as useful.

In order to inspect the mail queue, use one of the following commands:

$ mailq

$ sendmail -bp

$ postqueue -p

See also the "Care and feeding" section 12 below.

9 - Running Postfix instead of Sendmail

Prior to installing Postfix you should save any existing sendmail program files as described in section 6. Be sure to keep the old sendmail running for at least a couple days to flush any unsent mail. To do so, stop the sendmail daemon and restart it as:

# /usr/sbin/sendmail.OFF -q

Note: this is old sendmail syntax. Newer versions use separate processes for mail submission and for running the queue.

After you have visited the "Mandatory configuration file edits" section below, you can start the Postfix system with:

# postfix start

or, if you feel nostalgic, use the Postfix sendmail command:

# sendmail -bd -qwhatever

and watch your maillog file for any error messages. The pathname is /var/log/maillog, /var/log/mail, /var/log/syslog, or something else. Typically, the pathname is defined in the /etc/syslog.conf file.

$ egrep '(reject|warning|error|fatal|panic):' /some/log/file

Note: the most important error message is logged first. Later messages are not as useful.

In order to inspect the mail queue, use one of the following commands:

$ mailq

$ sendmail -bp

$ postqueue -p

See also the "Care and feeding" section 12 below.

10 - Mandatory configuration file edits

Note: the material covered in this section is covered in more detail in the BASIC_CONFIGURATION_README document. The information presented below is targeted at experienced system administrators.

10.1 - Postfix configuration files

By default, Postfix configuration files are in /etc/postfix. The two most important files are main.cf and master.cf; these files must be owned by root. Giving someone else write permission to main.cf or master.cf (or to their parent directories) means giving root privileges to that person.

In /etc/postfix/main.cf, you will have to set up a minimal number of configuration parameters. Postfix configuration parameters resemble shell variables, with two important differences: the first one is that Postfix does not know about quotes like the UNIX shell does.

You specify a configuration parameter as:

/etc/postfix/main.cf:
    parameter = value

and you use it by putting a "$" character in front of its name:

/etc/postfix/main.cf:
    other_parameter = $parameter

You can use $parameter before it is given a value (that is the second main difference with UNIX shell variables). The Postfix configuration language uses lazy evaluation, and does not look at a parameter value until it is needed at runtime.

Whenever you make a change to the main.cf or master.cf file, execute the following command in order to refresh a running mail system:

# postfix reload

10.2 - Default domain for unqualified addresses

First of all, you must specify what domain will be appended to an unqualified address (i.e. an address without @domain.tld). The "myorigin" parameter defaults to the local hostname, but that is probably OK only for very small sites.

Some examples (use only one):

/etc/postfix/main.cf:
    myorigin = $myhostname    (send mail as "user@$myhostname")
    myorigin = $mydomain      (send mail as "user@$mydomain")

10.3 - What domains to receive locally

Next you need to specify what mail addresses Postfix should deliver locally.

Some examples (use only one):

/etc/postfix/main.cf:
    mydestination = $myhostname, localhost.$mydomain, localhost
    mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
    mydestination = $myhostname

The first example is appropriate for a workstation, the second is appropriate for the mailserver for an entire domain. The third example should be used when running on a virtual host interface.

10.4 - Proxy/NAT interface addresses

The proxy_interfaces parameter specifies all network addresses that Postfix receives mail on by way of a proxy or network address translation unit. You may specify symbolic hostnames instead of network addresses.

IMPORTANT: You must specify your proxy/NAT external addresses when your system is a backup MX host for other domains, otherwise mail delivery loops will happen when the primary MX host is down.

Example: host behind NAT box running a backup MX host.

/etc/postfix/main.cf:
    proxy_interfaces = 1.2.3.4 (the proxy/NAT external network address)

10.5 - What local clients to relay mail from

If your machine is on an open network then you must specify what client IP addresses are authorized to relay their mail through your machine into the Internet. The default setting includes all subnetworks that the machine is attached to. This may give relay permission to too many clients. My own settings are:

/etc/postfix/main.cf:
    mynetworks = 168.100.189.0/28, 127.0.0.0/8

10.6 - What relay destinations to accept from strangers

If your machine is on an open network then you must also specify whether Postfix will forward mail from strangers. The default setting will forward mail to all domains (and subdomains of) what is listed in $mydestination. This may give relay permission for too many destinations. Recommended settings (use only one):

/etc/postfix/main.cf:
    relay_domains =            (do not forward mail from strangers)
    relay_domains = $mydomain  (my domain and subdomains)
    relay_domains = $mydomain, other.domain.tld, ...

10.7 - Optional: configure a smart host for remote delivery

If you're behind a firewall, you should set up a relayhost. If you can, specify the organizational domain name so that Postfix can use DNS lookups, and so that it can fall back to a secondary MX host when the primary MX host is down. Otherwise just specify a hard-coded hostname.

Some examples (use only one):

/etc/postfix/main.cf:
    relayhost = $mydomain
    relayhost = [mail.$mydomain]

The form enclosed with [] eliminates DNS MX lookups.

By default, the SMTP client will do DNS lookups even when you specify a relay host. If your machine has no access to a DNS server, turn off SMTP client DNS lookups like this:

/etc/postfix/main.cf:
    disable_dns_lookups = yes

The STANDARD_CONFIGURATION_README file has more hints and tips for firewalled and/or dial-up networks.

10.8 - Create the aliases database

Postfix uses a Sendmail-compatible aliases(5) table to redirect mail for local(8) recipients. Typically, this information is kept in two files: in a text file /etc/aliases and in an indexed file /etc/aliases.db. The command "postconf alias_maps" will tell you the exact location of the text file.

First, be sure to update the text file with aliases for root, postmaster and "postfix" that forward mail to a real person. Postfix has a sample aliases file /etc/postfix/aliases that you can adapt to local conditions.

/etc/aliases:
    root: you
    postmaster: root
    postfix: root
    bin: root
    etcetera...

Note: there should be no whitespace before the ":".

Finally, build the indexed aliases file with one of the following commands:

# newaliases
# sendmail -bi

11 - To chroot or not to chroot

Postfix daemon processes can be configured (via master.cf) to run in a chroot jail. The processes run at a fixed low privilege and with access only to the Postfix queue directories (/var/spool/postfix). This provides a significant barrier against intrusion. The barrier is not impenetrable, but every little bit helps.

With the exception of Postfix daemons that deliver mail locally and/or that execute non-Postfix commands, every Postfix daemon can run chrooted.

Sites with high security requirements should consider to chroot all daemons that talk to the network: the smtp(8) and smtpd(8) processes, and perhaps also the lmtp(8) client. The author's own porcupine.org mail server runs all daemons chrooted that can be chrooted.

The default /etc/postfix/master.cf file specifies that no Postfix daemon runs chrooted. In order to enable chroot operation, edit the file /etc/postfix/master.cf. Instructions are in the file.

Note that a chrooted daemon resolves all filenames relative to the Postfix queue directory (/var/spool/postfix). For successful use of a chroot jail, most UNIX systems require you to bring in some files or device nodes. The examples/chroot-setup directory in the source code distribution has a collection of scripts that help you set up Postfix chroot environments on different operating systems.

Additionally, you almost certainly need to configure syslogd so that it listens on a socket inside the Postfix queue directory. Examples for specific systems:

FreeBSD:
# mkdir -p /var/spool/postfix/var/run
# syslogd -l /var/spool/postfix/var/run/log
Linux, OpenBSD:
# mkdir -p /var/spool/postfix/dev
# syslogd -a /var/spool/postfix/dev/log

12 - Care and feeding of the Postfix system

Postfix daemon processes run in the background, and log problems and normal activity to the syslog daemon. The names of logfiles are specified in /etc/syslog.conf. At the very least you need something like:

/etc/syslog.conf:
    mail.err                                    /dev/console
    mail.debug                                  /var/log/maillog

IMPORTANT: the syslogd will not create files. You must create them before (re)starting syslogd.

IMPORTANT: on Linux you need to put a "-" character before the pathname, e.g., -/var/log/maillog, otherwise the syslogd will use more system resources than Postfix does.

Hopefully, the number of problems will be small, but it is a good idea to run every night before the syslog files are rotated:

# postfix check
# egrep '(reject|warning|error|fatal|panic):' /some/log/file

The DEBUG_README document describes the meaning of the "warning" etc. labels in Postfix logging.