Assume direct TLS if SMTP autoconfig finds port 465.

Assume direct TLS if SMTP autoconfig finds port 465.

Technically, this is incorrect:
A direct TLS-only SMTP service is against the standards,
and a "_submission._tcp" SRV record should have a port
that has a plaintext+STARTTLS service listening
(RFC 6186, section 3.1).

Port 465 shouldn't even be used for mail submission of
any kind, according to IANA:
(https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=465)

However, everyone ignores that, and port 465 is routinely
used for TLS-only SMTP service, and therefore it is safe to
assume direct TLS instead of STARTTLS.