For a mail relay server running only Postfix, I am making an educated guess that the only potentially needed open ports would be 25, 465, 587, and 2525 (According to https://sectigostore.com/blog/what-is-a-secure-smtp-ssl-port-heres-what-to-know-about-smtp-security/)
No need to open imap(s) and/or pop3(s), right ?
