Re: [dmarc-ietf] ARC questions

John R Levine <johnl@taugh.com> Mon, 23 November 2020 19:28 UTC

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Date: 23 Nov 2020 14:28:18 -0500
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From: "John R Levine" <johnl@taugh.com>
To: "Michael Thomas" <mike@mtcc.com>
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Subject: Re: [dmarc-ietf] ARC questions
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> From what I can tell, the main thing that ARC is doing is binding an auth-res 
> to a dkim signature-like thing. But as I recall -- it's been a long time -- 
> there were ordering requirements ala received headers for where new 
> dkim-signatures and auth-res go in the header. Assuming my memory is correct, 
> that means you can reconstruct "what this looked like before i messed with 
> it" already by signing the incoming auth-res as part of the new DKIM 
> signature.
>
> Is there something more going on here?

Not really.  There are ordering rules but mail systems do not follow them 
reliably, DKIM signatures in practice are not ordered.  Also, A-R can be 
deleted in some situations, so ARC makes copies of them to be more robust 
in transit.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly