[dmarc-ietf] spec nit - subdomains reporting clarity

Tomki <tki@tomki.com> Sat, 22 June 2019 01:04 UTC

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From: Tomki <tki@tomki.com>
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Date: Fri, 21 Jun 2019 18:04:28 -0700
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Subject: [dmarc-ietf] spec nit - subdomains reporting clarity
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The spec appears to be unclear on how subdomains are to be reported - ie 
most but not all implementations have performed this as intended, in the 
same XML as the top level domain (when the subdomain does not have its 
own DMARC TXT record)

Cisco interpreted the current definition to mean that every subdomain 
seen should get its own XML file. (not just the ones with their own 
DMARC record)  This results in every individual IronPort system [which 
has DMARC reporting enabled] generating hundreds to thousands of extra 
reports every day.
This can result in corporate reporters like Paypal or Rolls Royce 
(IronPort users) sending as many reports in a given day as Google.

The section which should be referred to in implementing a reporting 
engine is 7.2 https://tools.ietf.org/html/rfc7489#section-7.2
The only relevant bullet that I find here is
" The report SHOULD include the following data:"
...
   "Data for each Domain Owner's subdomain separately from mail from
       the sender's Organizational Domain, even if there is no explicit
       subdomain policy"

In trying to find out why Cisco implemented their reporting in the way 
that they did, I've actually had a hard time understanding how others 
understood that bullet point well enough - I can only imagine that 
everybody just implemented by following examples of existing 
implementations.

A suggested rewording for that bullet point:
" Data for each Domain Owner's subdomains as separate records in a 
report titled for the Organizational Domain, unless there is an explicit 
subdomain policy - in which case a standalone report is generated for 
that subdomain"

--Tomki