Re: [dmarc-ietf] ARC vs reject

Michael Thomas <mike@mtcc.com> Sat, 05 December 2020 21:13 UTC

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To: John Levine <johnl@taugh.com>, dmarc@ietf.org
References: <20201205210351.DB78E2904420@ary.qy>
From: Michael Thomas <mike@mtcc.com>
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Date: Sat, 5 Dec 2020 13:13:02 -0800
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Subject: Re: [dmarc-ietf] ARC vs reject
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On 12/5/20 1:03 PM, John Levine wrote:
> There are, however, use
>> cases where that is exactly wrong and in no case does the originating
>> domain want such an override to happen. Consider my bank sending me
>> transactional email. If somehow somebody managed to get that mail
>> through a mailing list and arc-resigned it, my bank does *not* want that
>> mail to be delivered regardless of the reputation of the mailing list
>> because something weird and wrong is happening on its face.
>   
> If you get a message from a bank via a trustworthy mailing list with a
> valid ARC chain that starts with a DMARC pass, that means someone at
> the bank really did send the message to the list. I don't think it's
> our job to try to guess whether the bank's users are following some
> internal policy we can't see.

There is no guarantee of that. If my bank says reject that mail, I want 
my provider to reject that mail, period. No amount of ARC shenanigans 
should change that policy.

>
> In practice, I can tell you that many organizations publish p=reject
> because it is "more secure" and have no clue about mailing lists, so
> it's a feature that ARC lets their users participate in mailing lists
> without totally ignoring their DMARC policy.

I'm not talking about misconfigured mail systems. I'm talking about a 
policy state that is not in the current set of p values.

Mike