Hi, we use:
25 - SMTP (TLS)
110 - POP (TLS)
143 - IMAP (TLS)
465 - Submission (SSL)
587 - Submission (TLS)
993 - IMAP (SSL)
995 - POP (SSL)
I think this ports layout is kinda the standard ports configuration for a mail service.
Note: The TLS ports accept both clear and secure connections (explicit TLS using STARTTLS). The SSL ports accept only secure connections (implicit SSL).
Sébastien Riccio
System & Network Admin
https://swisscenter.com