[dmarc-ietf] Description of 'n' value for the 'psd' tag AND/OR Clarify the Tree Walk

[Todd Herr <[e-mail]>]

Colleagues,

DMARCbis currently describes the value of 'n' for the 'psd' tag in a policy
record as follows:

The DMARC policy record is published for a PSD, but it is not the
Organizational Domain for itself and its subdomain. There is no need to put
psd=n in a DMARC record, except in the very unusual case of a parent PSD
publishing a DMARC record without the requisite psd=y tag.
I don't think this is entirely accurate, especially the second sentence
("no need ... except in the very unusual case"), and here's why. Either
that, or the description of the Tree Walk needs to be changed.

The Tree Walk is intended for both DMARC Policy discovery and
Organizational Domain discovery, and section 4.7 (DMARC Policy Discovery)
says the policy to be applied will be the DMARC record found at one of
these three locations:

   - The RFC5322.From domain
   - The Organizational Domain of the RFC5322.From domain
   - The Public Suffix Domain of the RFC5322.From domain

Meanwhile, section 4.8, Organizational Domain Discovery, gives the
following three options for where the Organizational Domain is:

   1. DMARC record with psd=n
   2. The domain one level below the domain with a DMARC record with the
   tag psd=y
   3. The record for the domain with the fewest number of labels.

The Tree Walk, as described in section 4.6, defines two explicit places to
stop, both of which rely on discovery of a DMARC policy record with a psd
tag defined:

   - Step 2, if the DMARC record has psd=n
   - Step 7, if the DMARC record has psd=n or psd=y

There is no other stopping place described, and no instructions to collect
DMARC policy records that don't have the psd tag defined during the walk,
and while Organizational Domain Discovery speaks of records retrieved
during the Tree Walk, there are no instructions in the Tree Walk steps
themselves in section 4.6 to put all the DMARC records with no psd tag in a
basket somewhere for later usage.

So the questions I have are...

   1. Should the description of the 'n' value for the 'psd' tag be updated
   to discuss its usage in a decentralized control model (e.g., seven label
   RFC5322.From with DMARC policy published at a five label name to allow for
   "local" control, with said policy being different from the policy published
   at the "traditional" org domain leve)?
   2. Should the description of the Tree Walk in section 4.6 be updated, to
   mention that valid DMARC records with no explicit psd tag might be found
   during the walk, and these should be preserved for later comparison to
   determine the organizational domain?

I look forward to the discussion.

-- 

Todd Herr | Technical Director, Standards & Ecosystem
Email: [e-mail]
Phone: [phone]


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