One new-ish data point: I believe Hotmail is leveraging the ADSP records from
domains they trust to be operating with consistency.
As has often been pointed out, if it's domains you already know
something about, you don't need ADSP.
ADSP is only the most obvious of assertions that people make about the
mail they send. If you don't know the sender, you can't believe the
assertions, so they're useless. If you do know the sender, you don't
need the assertions, so they're not useful.
This is why x= is either useless ot not useful.
R's,
John
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