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

Jeremy Harris <jgh@wizmail.org> Sun, 26 April 2020 10:24 UTC

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To: ietf-smtp@ietf.org
From: Jeremy Harris <jgh@wizmail.org>
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Date: Sun, 26 Apr 2020 11:24:47 +0100
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Subject: [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?

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