Re: [ietf-smtp] MTA-MTA SMTP and TLS-on-connect

Ned Freed <ned.freed@mrochek.com> Sun, 26 April 2020 14:24 UTC

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Date: Sun, 26 Apr 2020 07:17:41 -0700 (PDT)
From: Ned Freed <ned.freed@mrochek.com>
In-reply-to: "Your message dated Sun, 26 Apr 2020 11:24:47 +0100" <8d3d7446-db7d-ac04-2a36-258643254630@wizmail.org>
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To: Jeremy Harris <jgh@wizmail.org>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf-smtp/fS6JwdD53qkrjwSvumtQAcEpTQY>
Subject: Re: [ietf-smtp] MTA-MTA SMTP and TLS-on-connect
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> Hi,

> Noting that https://tools.ietf.org/html/draft-sheffer-uta-rfc7525bis-00
> section 3.2 says that TLS-on-connect SHOULD be preferred over STARTTLS
> (my rephrasing) - and that while T-o-c is reasonably common for MSA-MTA
> but not for MTA-MTA -

> should we think about technical means to facilitate the latter?

Absolutely not. Relaying mail is complicated enough already; adding another
port and DNS lookup to the mix and all the associated failure modes consistutes
a huge cost with no real benefit.

				Ned

> Eg:
> - a new well-known port (vs. TCP/25)
> - a DNS SRV label extending RFC 6816, to advertise a port
>   with the facility    (NB: RFC 8314 defines a "submissions" label)
> - some clever means for autodetect on a single port
> - an extension to DANE (RFC 7671) to bundle the port with the
>   cert-association
> --
> Cheers,
>   Jeremy

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