How to run Postfix on multiple SMTP ports on a Plesk server

Question

How to run Postfix on multiple SMTP ports on a Plesk server?

Answer

In this example, an alternate SMTP port 2525 is added in addition to default SMTP port 25.

Note: The master.cf file may be overwritten by Plesk update/upgrade.

1. Connect to a Linux server via SSH.

2. Create a backup file of the current master.cf file:

   # cp /etc/postfix/master.cf /etc/postfix/master.cf.bak

3. Open the file /etc/postfix/master.cf in any text editor. In this example, we are using the vi editor:

   # vi /etc/postfix/master.cf

4. Add a line with a new SMTP port like this:

   ==========================================================================
   # service type  private unpriv  chroot wakeup  maxproc command + args
   #               (yes)   (yes)   (yes)  (never) (100)
   # ==========================================================================
   smtp      inet  n       -       y      -       -       smtpd
   2525      inet  n       -       y      -       -       smtpd

5. Save the changes and close the file.

6. Restart Postfix to apply the changes:

   # service postfix restart

7. Verify that the new the SMTP port is listening:

   # netstat -plutn | grep 2525
   tcp 0 0 0.0.0.0:2525 0.0.0.0:* LISTEN 2996/master
   tcp6 0 0 :::2525 :::* LISTEN 2996/master

8. If a firewall is enabled on the server, make sure the new port is opened in firewall configuration.