and the dummy SMTP server works, but it consumes resources on the
host and eats bandwidth on the network. having a way to say "don't
send this host any mail" in DNS seems like a useful thing. and we
simply don't need the fallback to AAAA because we don't have the
backward compatibility issue that we had when MX records were
introduced.
Not sanctioning IPv6 AAAA records as an MX fall-back avoids the
undesired traffic now caused by SMTP spoofing of A records. MX
records might then be seen as an opt-in mechanism from the perspective
of IPv6, since opt-out mechanism are onerous for those not wishing to
participate. While Bill and others expressed concerns of being tied
to DNS, whatever replaces DNS must also offer separate service and IP
address resolution mechanisms.
there are lots of cases where I'd share the concern that DNS gets out of
sync with reality. but having this information in DNS doesn't bother me
in this case because the servers to which incoming mail messages to
user(_at_)example(_dot_)com are supposed to be sent, are a property of the
example.com domain, far more than a property of any host. it makes
sense to put information about a domain in DNS (or whatever might
someday replace DNS).
Keith
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