Why is it sufficient for the domain to have no RR relevant to email,
just as long as it has some RR?
Because it just seems the path of least resistance. If I were to
suggest that every domain taken from From: needs to have an MX RR then
somebody would point out that this violates SMTP RFC 2821 Section 5
which, in it's wisdom, treated the need for MX RR's as an optional "we
think it's a good idea" type of thing.
Arvel
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