Port 465
The TCP port for message submission over implicit TLS (RFC 8314): the TLS handshake starts as soon as the connection opens, before any SMTP command.
What it means
Port 465 was briefly registered as smtps, then revoked and reassigned, while widely used mail software kept using it for secure submission. RFC 8314 (2018) registered it again for the submissions service and recommends implicit TLS for mail programs, while asking providers to support STARTTLS on port 587 as well during the transition.
On 465 the client and server negotiate TLS first and then run ordinary submission inside the encrypted channel: EHLO, AUTH, MAIL FROM and so on. Nothing is ever exchanged in clear text, so there is no STARTTLS offer for an attacker to strip. Port 465 is for submission only; delivery between servers stays on port 25.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 8314, section 3.3: Implicit TLS for SMTP Submissionrfc-editor.org
- RFC 8314, section 7.3: Submissions Port Registrationrfc-editor.org
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