SMTPS

wikipedia:SMTPS (it was TCP port number 465 using TLS)

See also

• Port 587, is the default mail submission port. When an email client or outgoing server is submitting an email to be routed by a proper mail server, it should always use SMTP port 587 as the default port.

See also

• Mail, SMTP, submission, SMTPS, POP, IMAP, StartTLS, Exim, Postfix, IRedMail, Fail2ban, Dovecot, Roundcube, DKIM, SPF, DMARC, MX, ssmtp, mailx

https://www.mailgun.com/blog/which-smtp-port-understanding-ports-25-465-587/