Re: [dmarc-ietf] Nonexistent Domain Policy was: Re: Working Group Last Call: draft-ietf-dmarc-psd

Scott Kitterman <sklist@kitterman.com> Sun, 21 July 2019 16:53 UTC

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Date: Sun, 21 Jul 2019 16:53:35 +0000
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From: Scott Kitterman <sklist@kitterman.com>
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Subject: Re: [dmarc-ietf] Nonexistent Domain Policy was: Re: Working Group Last Call: draft-ietf-dmarc-psd
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On July 21, 2019 4:40:49 PM UTC, Alessandro Vesely <vesely@tana.it>; wrote:
>On Wed 17/Jul/2019 08:26:25 +0200 Scott Kitterman wrote:
>
>> Keep in mind that senders do send from what we call non-existent
>domains for
>> reasons that seem good and sufficient to them.  Let's take that as a
>fact,
>> whether it makes sense to us or not.
>
>
>Fair enough.  Let me quote the current spec:
>
>A.4.  Domain Existence Test
>
>   A common practice among MTA operators, and indeed one documented in
>   [ADSP], is a test to determine domain existence prior to any more
>  expensive processing.  This is typically done by querying the DNS for
>   MX, A, or AAAA resource records for the name being evaluated and
>   assuming that the domain is nonexistent if it could be determined
>   that no such records were published for that domain name.
>
>   The original pre-standardization version of this protocol included a
>   mandatory check of this nature.  It was ultimately removed, as the
>   method's error rate was too high without substantial manual tuning
>   and heuristic work.  There are indeed use cases this work needs to
>   address where such a method would return a negative result about a
>   domain for which reporting is desired, such as a registered domain
>   name that never sends legitimate mail and thus has none of these
>   records present in the DNS.

Yes, but that was for a different use case.  It was , AIUI, considered that reporting could be skipped on such 'non-existant' domains, but that proved problematic since such domains as these are used in mail.

'np' doesn't have the same issue.  It uses non-existence in a positive (do some processing) not a negative sense (reporting can be skipped for these), so the problems described in that paragraph are not only not relevant, the paragraph supports the case for 'np'.

Scott K