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

Alessandro Vesely <> Sun, 21 July 2019 16:40 UTC

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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 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.