Re: [dmarc-ietf] Ticket #1 - SPF alignment

Alessandro Vesely <vesely@tana.it> Thu, 28 January 2021 12:13 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Date: Thu, 28 Jan 2021 13:13:00 +0100
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Subject: Re: [dmarc-ietf] Ticket #1 - SPF alignment
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On Wed 27/Jan/2021 20:24:05 +0100 Scott Kitterman wrote:
> On Wednesday, January 27, 2021 12:25:59 PM EST Alessandro Vesely wrote:
>> 
>> Can we fix this aberration?
>> 
>> The spec needs a fix anyway, because from the text I quoted above I
>> understood that the example message passes DMARC.  Am I the only one?
>> 
>> In addition, as I said, SPF filters are likely to report HELO as helo and
>> MAIL FROM as mailfrom.  If we want to carry over this quirk, the spec must
>> say that a DMARC filter which gathers SPF authentication status from an
>> upstream filter MUST make sure that mailfrom is empty before validating
>> based on an aligned helo.
>> 
>> Dropping that absurd discrimination between SPF identifiers would make for a
>> smoother spec.  Since non-null mailfroms are in most cases aligned with
>> either From: or helo, the differences between existing compliant
>> implementations and the smoother spec would be limited to a hardly
>> noticeable set of test messages.
> 
> Your absurd is my eminently reasonable.
> 
> I can't explain why it was added, but it makes sense, IMO, to have it there to
> aid in reconstructing the exact situation for trouble shooting purposes.


Can you expand on how ignoring helo aids trouble shooting?


> DMARC has always (for the SPF related portion) been about alignment of mail
> from and from.  I don't think adding HELO has appreciable value and is
> certainly not worth the added complexity to implement DMARC to include.


 From an implementer POV, the complication stays in the idiosyncratic 
identifier processing.  I wonder how many do follow it strictly.  IMHO, a 
reasonable DMARC spec should either smooth out the discrimination or provide a 
clear explanation of why such peculiar processing is needed and what would 
happen if all identifiers were treated equal.


> There are lots of ways that DMARC could have addressed SPF.  Personally I
> thought it might make sense to skip using the mail from SPF result and just
> check if the from address would pass if it were subjected to an SPF check, but
> that's not the existing design.  I don't think it should be changed now.


Yeah, after you insisted, I vaguely recollected about an SPF argument that I 
had erased from memory.  I can't recall its merit.

DKIM'S d= are domains, and DKIM scope is exactly to identify a domain.  That's 
more akin to helo than mail from.


Best
Ale
--