On Tue 02/Aug/2022 14:33:21 +0200 Barry Leiba wrote:
I think it is useful to include a brief explanation of why we moved away
from the PSL, because that was in the previous version. But we should
be very tightly focused when we give any such background, to avoid
creating distractions.
Here's one more attempt at proposing the text of a complete, free-standing
section:
There is no general rule to determine domain prefixes. The PSL is the
result of the ongoing, ponderous work of a group of volunteers who
examine each case. However, DMARC users define DMARC records at their
Organizational Domain, so it is possible to discover them based on
that. Here we define an algorithm that determines the Organizational
Domain for DMARC purposes. For established prefixes, the result is the
same as using the PSL.
Given a DNS Tree Walk (#dns-tree-walk) which retrieved at least one
DMARC record, determine the Organizational Domain by applying the
following rules, from the longest domain toward the shortest one:
1. If a valid DMARC record contains the psd= tag set to 'n' (psd=n),
this is the Organizational Domain and the selection process is
complete.
2. If a valid DMARC record, other than the one for the domain where
the tree walk started, contains the psd= tag set to 'y' (psd=y),
the Organizational Domain is the domain one label below this one
in the DNS hierarchy, and the selection process is complete.
3. Otherwise select the record for the domain with the fewest number
of labels. This is the Organizational Domain and the selection
process is complete.
Best
Ale
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