Postfix

Installation

Most distributions include a postfix package.

The daemon (named master) is started by running:

postfix start

Within a container

The bad news is that the Postfix service is designed to be launched from userspace using postfix(1), rather than being a binary that can be invoked in the foreground. This defies the architecture of modern containers.

The good news is that running Postfix in a standalone container is barely useful. Postfix will likely need to run alongside at least one other service. The solution to both issues is running a supervisor.

Consider the following configuration for Supervisord:

[supervisord]
childlogdir=/var/log/supervisord
logfile=/dev/stderr
logfile_maxbytes=0
nodaemon=true
user=root

[program:postfix]
autostart=false
command=postfix start
startsecs=0
redirect_stderr=true

Configuration

Administration

Testing the service

Install mailx and send an empty email.

To test mail relay to external hosts, try:

mail -s 'Test Email' '[email protected]' </dev/null

Reviewing the queue

Two useful administrative utilities exist for reviewing the mail queue: postqueue(1) and postcat(1).

To view the mail queue, try:

postqueue -p

This will display the queued messages, the senders and recipients, and a mail ID.

To force all queued mail to be sent now, run:

postqueue -f

To instead force a singular message to be send now, run:

postqueue -i MAILID

To instead inspect a message in the queue, try:

postcat -vq MAILID

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