Re: [dmarc-ietf] ARC questions

Michael Thomas <mike@mtcc.com> Sun, 22 November 2020 19:29 UTC

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To: John R Levine <johnl@taugh.com>, "Kurt Andersen (b)" <kboth@drkurt.com>
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From: Michael Thomas <mike@mtcc.com>
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Date: Sun, 22 Nov 2020 11:29:26 -0800
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Subject: Re: [dmarc-ietf] ARC questions
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On 11/22/20 11:14 AM, John R Levine wrote:
>> Is there a reason that there is a separate ARC-signature rather than 
>> just using the DKIM signature that is normally created for the new 
>> message? Since ARC is new, you'd not want the intermediary to stop 
>> DKIM signing the message so you end up with essentially two 
>> signatures doing essentially the same thing?
>
> The ARC signature has a sequence number so you can track the chain of 
> custody.  You are right that it is similar to the DKIM signature but 
> the extra ovehead doesn't seem excessive.
>
Did the wg consider just grafting that onto the DKIM signature itself 
instead of having essentially a duplicate signature? Receivers are 
already supposed to ignore any tags they don't understand so it 
shouldn't hurt backward compatibility.

Mike