Re: [Shutup] [ietf-smtp] Fwd: New Version Notification for draft-fenton-smtp-require-tls-00.txt

Jim Fenton <> Mon, 11 January 2016 19:26 UTC

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To: John Levine <>,,
References: <20160111163401.48404.qmail@ary.lan>
From: Jim Fenton <>
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Subject: Re: [Shutup] [ietf-smtp] Fwd: New Version Notification for draft-fenton-smtp-require-tls-00.txt
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On 1/11/16 8:34 AM, John Levine wrote:
>>> Only sort of.  In this case, the downgrade path is obvious, you
>>> ignore the TLS flag and send the message along.
>> That's the opposite of the goal here. SMTP makes tries to delivery
>> messages, even if that results in a downgrade in security. The goal here
>> is to fail the transmission of REQUIRETLS tagged messages that can't be
>> sent in accordance with the originator's security requirements.
> Of course, but there's no reason for recipient MTAs to pay any
> attention to the tag if they don't want to.  There is no penalty to
> them for doing so.  With EAI there's at least the penalty of messages
> getting smashed.

Misbehavior by MTAs is outside the scope of the threat model for SMTP
TLS. I have already described how such behavior could be detected; the
erosion of trust resulting from that is likely to be harmful to the mail
provider's business model.