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Re: [dmarc-ietf] non-mailing list use case for differing header domains

Alessandro Vesely <vesely@tana.it> Tue, 28 July 2020 15:15 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Date: Tue, 28 Jul 2020 17:14:56 +0200
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Subject: Re: [dmarc-ietf] non-mailing list use case for differing header domains
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On Tue 28/Jul/2020 11:07:19 +0200 Laura Atkins wrote:
>> On 28 Jul 2020, at 08:36, Alessandro Vesely <vesely@tana.it wrote:
>> On Tue 28/Jul/2020 08:54:02 +0200 Autumn Tyr-Salvia wrote:

>>> # The resulting message uses executive@secondbrand.com in the friendly
>>> From: field, but firstbrand.com  in the SMTP MAIL FROM domain, so the 
>>> headers are no longer aligned for SPF. >>> #
>>
>> Heck, can't they DKIM sign?
> 
> This really misses Autumn’s point. [...]
> 
> Autumn has presented a very real world scenario that demonstrates the
> overall complexity of mail management operationally. Your solution “sign
> with DKIM” has significant barriers to adoption. For instance, assume that
> there is code installed on the mailserver that will grab the 5322.from
> address and sign with the appropriate DKIM key. How many domains are
> involved? How many different mailservers? How long will this solution take
> to deploy? Banks do not move quickly and, for the obvious reasons, any
> changes to security require multiple reviews and assurances that the
> implications are understood.


If the bank delegates a subdomain to each trusted subsidiary, each subsidiary 
could manage their keys on their local DNS and email servers.  If the bank can 
afford "relaxed" DKIM alignment, they can sign with d=local-branch.bank.example 
and From: transactions@bank.example.  What's the risk of doing so?


Best
Ale
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