Mailserver Port Numbers

Following are port numbers for different services:

• SMTP – 25 (465 with SSL, 587 with TLS)
• POP3 – 110 (995 for SSL)
• IMAP – 143 (993 for SSL)
• ManageSieve – 4190 (Gmail-like mail filtering)
• Amavis – 10025 (spam/antivirus checks)

You can find/verify ports used by postfix and dovecot using following commands:

netstat -tulpn | egrep 'master|dovecot'

Above command assumes you are using postfix (master) and dovecot. You can replace them with your packages or even port number like:

netstat -tulpn | egrep '25|465|587|110|143'

Please note that if you are using non standard ports, you may miss open-ports when running a command-like above.