Postfix - Architecture (Processes)

About

postfix may starts several process, generally:

• one to receive and relay mail (port 25)
• one to submit mail (port 587)

Remotely

Master

Postfix services are implemented by daemon processes. These run in the background, started on-demand by the master(8) process.

• Check that the port is taken locally by the master postfix process

 netstat -tulpn | egrep 'master|:25'

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      31278/master
tcp6       0      0 :::25                   :::*                    LISTEN      31278/master

See Postfix - Configuration (File, List and Default values)

More http://www.postfix.org/master.5.html

Configuration

There is a lot of configuration that you can see with their default value on this page.

Port 25

• It needs to be open in order for it to receive mail from the internet.
• It should accept anonymous connections, but not for relaying

The process on port 25 is the default and is defined in the smtp line of the master.cf

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       n       -       -       smtpd

It follows all configuration defined in the /etc/postfix/main.cf file.

• Enable Postfix - TLS (SSL) configuration

Port 587

Port 587

• is considered a submission port. It is also what clients use to send mail out using your server.
• should only allow authenticated connections

See: What are the SMTP Ports? (25, 465, 587)