Re: [dmarc-ietf] ARC questions

Michael Thomas <mike@mtcc.com> Wed, 02 December 2020 20:38 UTC

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To: John R Levine <johnl@taugh.com>, Brandon Long <blong@google.com>
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From: Michael Thomas <mike@mtcc.com>
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Date: Wed, 2 Dec 2020 12:38:31 -0800
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Subject: Re: [dmarc-ietf] ARC questions
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On 12/2/20 12:35 PM, John R Levine wrote:
> On Wed, 2 Dec 2020, Michael Thomas wrote:
>>>> different in that respect. In fact as far as I can tell they are 
>>>> identical modulo the i= difference.
>>>
>>> Please reread the ARC spec.  The ARC-Authentication-Results at level 
>>> N tells you whether the ARC and DKIM signatures were good at level N-1.
>
>> That's why I said "modulo the i= difference"
>
> Well, yeah.  That i= is why we have ARC seals rather than just using a 
> DKIM signature.
>
> Remember that ARC is only useful if the last system sending the 
> message to you is reasonably trustworthy, not in the sense that it 
> never sends spam, but in the sense that its ARC tells the truth about 
> what it saw.  That's a low bar that any mailing list should be able to 
> meet.
>
Which could trivially be added as an extension to DKIM and Auth-Res 
negating the need for the Seal altogether since DKIM can directly sign 
the old (renamed) auth-res. I can understand for an experiment not 
wanting to touch dkim or auth-res, but for something standards track 
less is more.

Mike