John Levine wrote:
Not to be cynical or anything, but regardless of what we decree, I
think it's vanishingly unlikely that many systems on the public
Internet* will accept mail from a domain with only an AAAA record.
I think it's vanishing unlikely that email will be useful at all, if
filter writers keep trashing mail based on such dubious criteria.
Not to reignite the usual spam argument, but it is (unfortunately in
case) not 1988 or even 1998 any more. When upwards of 90% of all mail
spam, keeping mail usable is at least as dependent on limiting the spam
that shows up in people's mailboxes as delivering the trickle of good
Real life spam filters use metrics and tune to the actual behavior of
mailers. If most of the mail that comes from domains with AAAA and no
is spam, they'll tune for that, and it won't be a mistake. For the
forseeable future, most such mail will be from zombies, and it'll all
This document is not the place to fight spam. If you want a BCP to deprecate
the fall-back, then write one. Until all the implementations remove
fall-back to A, the correct behavior is to also fall-back to AAAA. People
(particularly the apps dev & support communities) are having a hard enough
time getting their heads around even thinking about IPv6 that making your
proposed procedural change is insane. Whatever reasons people have for not
implementing MX will not change just because they are deploying IPv6.
The current text is just fine the way it is.
IETF mailing list