Updated: 2021/Apr/14

POSTFIX-WRAPPER(5)            File Formats Manual           POSTFIX-WRAPPER(5)

       postfix-wrapper - Postfix multi-instance API

       Support for managing multiple Postfix instances is available as of
       version 2.6. Instances share executable files and documentation, but
       have their own directories for configuration, queue and data files.

       This document describes how the familiar "postfix start" etc. user
       interface can be used to manage one or multiple Postfix instances, and
       gives details of an API to coordinate activities between the postfix(1)
       command and a multi-instance manager program.

       With multi-instance support, the default Postfix instance is always
       required. This instance is identified by the config_directory
       parameter's default value.

       Multi-instance support is backwards compatible: when you run only one
       Postfix instance, commands such as "postfix start" will not change
       behavior at all.

       Even with multiple Postfix instances, you can keep using the same
       postfix commands in boot scripts, upgrade procedures, and other places.
       The commands do more work, but humans are not forced to learn new

       For example, to start all Postfix instances, use:

              # postfix start

       Other postfix(1) commands also work as expected. For example, to find
       out what Postfix instances exist in a multi-instance configuration,

              # postfix status

       This enumerates the status of all Postfix instances within a
       multi-instance configuration.

       To manage a specific Postfix instance, specify its configuration
       directory on the postfix(1) command line:

              # postfix -c /path/to/config_directory command

       Alternatively, the postfix(1) command accepts the instance's
       configuration directory via the MAIL_CONFIG environment variable (the
       -c command-line option has higher precedence).

       Otherwise, the postfix(1) command will operate on all Postfix

       By default, the postfix(1) command operates in single-instance mode. In
       this mode the command invokes the postfix-script file directly
       (currently installed in the daemon directory).  This file contains the
       commands that start or stop one Postfix instance, that upgrade the
       configuration of one Postfix instance, and so on.

       When the postfix(1) command operates in multi-instance mode as
       discussed below, the command needs to execute start, stop, etc.
       commands for each Postfix instance.  This multiplication of commands is
       handled by a multi-instance manager program.

       Turning on postfix(1) multi-instance mode goes as follows: in the
       default Postfix instance's main.cf file, 1) specify the pathname of a
       multi-instance manager program with the multi_instance_wrapper
       parameter; 2) populate the multi_instance_directories parameter with
       the configuration directory pathnames of additional Postfix instances.
       For example:

                  multi_instance_wrapper = $daemon_directory/postfix-wrapper
                  multi_instance_directories = /etc/postfix-test

       The $daemon_directory/postfix-wrapper file implements a simple manager
       and contains instructions for creating Postfix instances by hand.  The
       postmulti(1) command provides a more extensive implementation including
       support for life-cycle management.

       The multi_instance_directories and other main.cf parameters are listed
       below in the CONFIGURATION PARAMETERS section.

       In multi-instance mode, the postfix(1) command invokes the
       $multi_instance_wrapper command instead of the postfix-script file.
       This multi-instance manager in turn executes the postfix(1) command in
       single-instance mode for each Postfix instance.

       To illustrate the main ideas behind multi-instance operation, below is
       an example of a simple but useful multi-instance manager


              : ${command_directory?"do not invoke this command directly"}

              instance_dirs=`$POSTCONF -h multi_instance_directories |
                              sed 's/,/ /'` || exit 1

              for dir in $config_directory $instance_dirs
                  case "$1" in
                      test "`$POSTCONF -c $dir -h multi_instance_enable`" \
                          = yes || continue;;
                      test "`$POSTCONF -c $dir -h multi_instance_enable`" \
                          = yes || {
                          $POSTFIX -c $dir check || err=$?
                  $POSTFIX -c $dir "$@" || err=$?

              exit $err

       Each Postfix instance has its own main.cf file with parameters that
       control how the multi-instance manager operates on that instance.  This
       section discusses the most important settings.

       The setting "multi_instance_enable = yes" allows the multi-instance
       manager to start (stop, etc.) the corresponding Postfix instance. For
       safety reasons, this setting is not the default.

       The default setting "multi_instance_enable = no" is useful for manual
       testing with "postfix -c /path/name start" etc.  The multi-instance
       manager will not start such an instance, and it will skip commands such
       as "stop" or "flush" that require a running Postfix instance.  The
       multi-instance manager will execute commands such as "check",
       "set-permissions" or "upgrade-configuration", and it will replace
       "start" by "check" so that problems will be reported even when the
       instance is disabled.

       Some files are shared between Postfix instances, such as executables
       and manpages, and some files are per-instance, such as configuration
       files, mail queue files, and data files.  See the NON-SHARED FILES
       section below for a list of per-instance files.

       Before Postfix multi-instance support was implemented, the executables,
       manpages, etc., have always been maintained as part of the default
       Postfix instance.

       With multi-instance support, we simply continue to do this.
       Specifically, a Postfix instance will not check or update shared files
       when that instance's config_directory value is listed with the default
       main.cf file's multi_instance_directories parameter.

       The consequence of this approach is that the default Postfix instance
       should be checked and updated before any other instances.

       Only the multi-instance manager implements support for the
       multi_instance_enable configuration parameter. The multi-instance
       manager will start only Postfix instances whose main.cf file has
       "multi_instance_enable = yes". A setting of "no" allows a Postfix
       instance to be tested by hand.

       The postfix(1) command operates on only one Postfix instance when the
       -c option is specified, or when MAIL_CONFIG is present in the process
       environment. This is necessary to terminate recursion.

       Otherwise, when the multi_instance_directories parameter value is
       non-empty, the postfix(1) command executes the command specified with
       the multi_instance_wrapper parameter, instead of executing the commands
       in postfix-script.

       The multi-instance manager skips commands such as "stop" or "reload"
       that require a running Postfix instance, when an instance does not have
       "multi_instance_enable = yes".  This avoids false error messages.

       The multi-instance manager replaces a "start" command by "check" when a
       Postfix instance's main.cf file does not have "multi_instance_enable =
       yes". This substitution ensures that problems will be reported even
       when the instance is disabled.

       No Postfix command or script will update or check shared files when its
       config_directory value is listed in the default main.cf's
       multi_instance_directories parameter value.  Therefore, the default
       instance should be checked and updated before any Postfix instances
       that depend on it.

       Set-gid commands such as postdrop(1) and postqueue(1) effectively
       append the multi_instance_directories parameter value to the legacy
       alternate_config_directories parameter value. The commands use this
       information to determine whether a -c option or MAIL_CONFIG environment
       setting specifies a legitimate value.

       The legacy alternate_config_directories parameter remains necessary for
       non-default Postfix instances that are running different versions of
       Postfix, or that are not managed together with the default Postfix


              When present, this forces the postfix(1) command to operate only
              on the specified Postfix instance. This environment variable is
              exported by the postfix(1) -c option, so that postfix(1)
              commands in descendant processes will work correctly.

       The text below provides only a parameter summary. See postconf(5) for
       more details.

       multi_instance_directories (empty)
              An optional list of non-default Postfix configuration
              directories; these directories belong to additional Postfix
              instances that share the Postfix executable files and
              documentation with the default Postfix instance, and that are
              started, stopped, etc., together with the default Postfix

       multi_instance_wrapper (empty)
              The pathname of a multi-instance manager command that the
              postfix(1) command invokes when the multi_instance_directories
              parameter value is non-empty.

       multi_instance_name (empty)
              The optional instance name of this Postfix instance.

       multi_instance_group (empty)
              The optional instance group name of this Postfix instance.

       multi_instance_enable (no)
              Allow this Postfix instance to be started, stopped, etc., by a
              multi-instance manager.


       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf
              configuration files.

       data_directory (see 'postconf -d' output)
              The directory with Postfix-writable data files (for example:
              caches, pseudo-random numbers).

       queue_directory (see 'postconf -d' output)
              The location of the Postfix top-level queue directory.

       postfix(1) Postfix control program
       postmulti(1) full-blown multi-instance manager
       $daemon_directory/postfix-wrapper simple multi-instance manager

       The Secure Mailer license must be distributed with this software.

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA