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

From: "John Levine" <[email-masked]>
Date: 11 Jan 2016 16:34:01 -0000

>> 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.

>But you make a good point about the fake MX problem: if you're concerned
>about DNS attacks, you need to make sure that the recipient domain, and
>not just the domain of the MX server, is DNSSEC protected. That's an
>oversight in the specification I will correct.

RFC 7672 which has already addressed that issue in great detail.

R's,
John

---

From: Jim Fenton <[email-masked]>
Date: Mon, 11 Jan 2016 11:25:28 -0800

> them for doing so.  With EAI there's at least the penalty of messages

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.

-Jim