Port 465: SMTPS with implicit TLS

Port 465 is the submission port with implicit TLS for authenticated mail sending.

Port: 465
Protocol: TCP
Service: SMTP Submission (implicit TLS)
Exposure: Public: yes, for mail clients

daniele@mikweb: ~/ports — less 465.md

On port 465 mail servers accept mail from clients with implicit TLS: the connection is encrypted from the first byte. Long labelled deprecated, it has been officially registered as submissions and recommended since RFC 8314 (2018).

Port 587 or 465? Both are correct. 465 is more robust because no STARTTLS downgrade is possible; 587 is supported by virtually every client. Ideally offer both, always with authentication.

Typical: client set to "STARTTLS" but configured with port 465 – the connection hangs until it times out. Port 465 needs "SSL/TLS".

Check

openssl s_client -connect mail.example.com:465 -crlf