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Re: /etc/services losses

Taylor R Campbell <> writes:

> `smtp(s)' and `submission(s)' are subtly different protocols and
> should not be aliases:
> - smtp(s) is for MTA<->MTA exchange of fully formed internet mail
>   messages with complete headers.
> - submission(s) is for an MUA to submit new messages, which may not
>   have complete headers or fully qualified addresses or otherwise be
>   fully formed, via a mail submission agent into the internet mail
>   system.

Yes, they are different, however my take from reading is that the orignal label
of 465 as smtps was confused, and that IANA now labels 465 as start

> I'm also not sure it matters if a TLS session is preceded by the ten
> bytes `STARTTLS\r\n' on the wire or not.

It very clearly does not matter.  I think the concern was
implementations that treated TLS as optional and would continue.  But
that's all rationale for why RFC8314 recommends as it does.  Where we
are now is that 465/tcp is submissions and 587 is submission.  And our
services file has smtps for 465, but that no longer exists in IANA-land.

> I'm not sure if there is any port number that can rightly be called
> `smtps' today.

Agreed.  I know of no usage that is MUA-to-MUA SMTP over prenegotiated
TLS.   It's basically a STARTTLS over 25 world -- which is what I think
you are thinkig

For this thread, I think all that matters is that we find a reasonable
way to update services to match IANA while maintaining local diffs.  We
have gotten into a bad state.

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