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

Ned Freed <ned.freed@mrochek.com> Sun, 26 April 2020 22:54 UTC

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Cc: ietf-smtp@ietf.org, jgh@wizmail.org
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Date: Sun, 26 Apr 2020 15:46:37 -0700 (PDT)
From: Ned Freed <ned.freed@mrochek.com>
In-reply-to: "Your message dated Sun, 26 Apr 2020 18:20:58 -0400" <20200426222058.DD30A1864B62@ary.qy>
References: <8d3d7446-db7d-ac04-2a36-258643254630@wizmail.org> <20200426222058.DD30A1864B62@ary.qy>
To: John Levine <johnl@taugh.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf-smtp/iEijw9su5EQS05bxyVrvML_SHLo>
Subject: Re: [ietf-smtp] MTA-MTA SMTP and TLS-on-connect
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> In article <8d3d7446-db7d-ac04-2a36-258643254630@wizmail.org> you write:
> >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?

> Turns out the STARTTLS language was in RFC 7525 and we missed it.

> If this draft goes anywhere, I think we should tell them to fix it and
> say that STARTTLS and TLS-on-connect are equivalent if the path with
> STARTTLS requires its use, which I think reflects reality.

Agreed. The converse should also be mentioned: There's no advantage to
TLS-on-connect if failure means falling back to an unencrypted port.

All of which is a roundabout way of saying there's actually no security
justification for TLS-on-connect for SMTP, RFC 7525 notwithstanding.

				Ned