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Re: QUIC vs. SMTP

Paul Vixie <paul@redbarn.org> Thu, 26 February 2026 17:04 UTC

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Date: Thu, 26 Feb 2026 18:04:11 +0100
From: Paul Vixie <paul@redbarn.org>
To: John R Levine <johnl@taugh.com>
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Subject: Re: QUIC vs. SMTP
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CC: Dan Wing <danwing@gmail.com>, quic@ietf.org
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Starttls, in both SMTP and IMAP, can be mitm'd (injection of refusal). We should not be using them any more.
Paul Vixie

Feb 26, 2026 17:57:47 John R Levine <johnl@taugh.com>:

> On Wed, 25 Feb 2026, Dan Wing wrote:
>> One approach would be take idea of https://datatracker.ietf.org/doc/html/rfc8314 and extend it include SMTP itself, which would bring QUIC along doing a happy eyeballs-like attempt at QUIC falling back to TLS-over-TCP falling back to TCP-port-25-STARTTLS falling back to TCP-port-25 plaintext, or as Martin suggested have DNS optimize those choices.
> 
> The problem with that is that SMTP doesn't do the TLS handshake at startup, only after a STARTTLS command in the TCP session.  But see next message.
> 
> R's,
> John

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