Is it possible to use another port for SMTP connection if 25 port is blocked by ISP?

Question

Is it possible to use another port for SMTP connection if 25 port is blocked by ISP?

Answer

Usually, ISP blocks only outgoing 25 port. There are two options:

• Contact ISP and ask to unblock 25 port for outgoing traffic.
• Setup relayhost(smarthost) in postfix following steps from any 3rd-party resource like this.

If ISP also blocks incoming 25 port, it will be impossible to use mail service on this server. Anyway, contact ISP for assistance.

Additional information

• For configuring Mail Submission port 587 in Plesk for Windows please refer to the article
• For configuring Mail Submission port 587 in Plesk for Linux please refer to the article

Note: Plesk server cannot be configured to use 587 port for outbound SMTP traffic. Either only 25 or 25 in conjunction with 587 can be used. Also, Plesk will still be listening on 25 port alongside with 587.