Re: [secdir] Review of draft-melnikov-smtp-priority-tunneling-03

Alexey Melnikov <> Thu, 19 July 2012 16:03 UTC

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Date: Thu, 19 Jul 2012 17:04:36 +0100
From: Alexey Melnikov <>
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Subject: Re: [secdir] Review of draft-melnikov-smtp-priority-tunneling-03
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Hi Shawn,

On 18/07/2012 08:00, Shawn Emery wrote:
> I have reviewed this document as part of the security directorate's 
> ongoing effort to review all IETF documents being processed by the 
> IESG. These comments were written primarily for the benefit of the 
> security area directors. Document editors and WG chairs should treat 
> these comments just like any other last call comments.
> This experimental draft describes a SMTP tunneling method to support 
> priority message values for Mail Transfer Agents (MTA) that don't 
> understand the MT-PRIORITY SMTP extension.
> The security consideration section does exist and is quite detailed in 
> listing the various attack scenarios and mitigating against these 
> attacks.  It goes on to provide exceptions of when MT-Priority header 
> values are not required to be stripped.  These have consequences such 
> as breaking DKIM signatures, assuming subsequent MTAs are compliant 
> with the new tunneling, or rejecting the messaging.  The document may 
> clarify on when it is acceptable to break DKIM signatures and/or 
> describe the environment.

I don't think I know a clear answer to this and this might be 
implementation/deployment specific.

> On the other hand, if the MSA/MTA decides to alter the message and 
> needs to resign the message then is there any ambiguity of what the 
> message/fields would be when resigned?

As far as this extension is concerned, there is only one header field of 
relevance. So I don't think so.

> General comments:
> Thanks for providing the before and after examples as this was helpful 
> in my understanding of the protocol.
> Editorial comments:
> s/Example of such/Examples of such/

Fixed in my copy.