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

Alessandro Vesely <vesely@tana.it> Tue, 02 February 2021 11:59 UTC

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To: John Levine <johnl@taugh.com>, dmarc@ietf.org
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From: Alessandro Vesely <vesely@tana.it>
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Subject: Re: [dmarc-ietf] Ticket #1 - SPF alignment
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On Tue 02/Feb/2021 00:11:54 +0100 John Levine wrote:
> In article <babf1538-5172-f101-d5e4-c4fa33dea495@tana.it> you write:
>>On Mon 01/Feb/2021 01:10:01 +0100 Scott Kitterman wrote:
>>> 
>>> SPF is what it is (RFC 7208).  DMARC doesn't need to re-invent the protocol
>>> (and shouldn't).  For any properly implemented SPF verifier, DMARC should be
>>> able to consume the Mail From result.
>>
>> Perhaps Courier-MTA is not so properly implemented, but when mail from is empty 
>> it just omits the corresponding Received-SPF: header field.
> 
> That's a peculiarity of Courier.


Yes.  Configured as at mine, it writes three Received-SPF: fields, for helo, 
mfrom, and, as a non-standard extension, for From:.  As I said, the one for 
mfrom is only written in case mfrom is not-empty.


> My MTA adds an SPF clause in the A-R header whether or not there's a null
> bounce address.

How can it report, say, fail for helo and pass for mfrom in just one clause?


>> OTOH, properly implemented SPF verifiers could skip producing a Mail From 
>> result if the helo identity was verified successfully.
> 
> No, they could not.  That's not what the SPF spec says.


                                If a conclusive determination about the
    message can be made based on a check of "HELO", then the use of DNS
    resources to process the typically more complex "MAIL FROM" *can* be
    avoided.
                         https://tools.ietf.org/html/rfc7208#section-2.3
                         (my emphasis)


Best
Ale
--