Is there a sufficiently useful degree of benefit to warrant the
(considerable) cost of development, deployment, and use?
What is this question in reference to? The notion of NXDOMAIN lookups
or ADSP in general?
Is the benefit long-term?
Assuming you're talking about ADSP in general, yes. Where-ever and
when-ever it is used, DKIM+ADSP can permanently detect the unauthorized
use of domain(s) in an email From: header, forever. The benefit is
A cousin domain is sufficiently trivial to use so as to make the intended
protection against use of sub-domains meaningless.
That is just a restatement of the view which asserts that because ADSP
can't protect domains you don't control you therefore needn't bother
protecting those you do.
So the question is what sort of mechanism is going to benefit from locking
sub-domains, but not cousin domains? How is the benefit meaningful?
I don't understand the question but I suspect it's a variant of what's
already been asked and answered. Is there something new here?
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