I got the following message and received permission to repost it here.
Tony Hansen
tony(_at_)att(_dot_)com
From: "Steinar H. Gunderson" <sesse(_at_)google(_dot_)com>
Hi,
Harald sent this on to me, as I've set up and help administer the a
real-world e-mail setup with IPv6 support. I'm not sure how much I can
help you with the other points, but I can tell you that there is at
least one site accepting e-mail with an AAAA record only -- my home
machine. :-)
Apart from that, I don't think you can remove delivering e-mail directly
to AAAA records; it's already supported in MTAs out there, and you can
be pretty sure it's actually being used. Besides, if you sent mail to
foo(_at_)example(_dot_)org, and example.org had both A and AAAA records (but no
MX), should you really not try delivering on IPv6?
/* Steinar */
-- Software Engineer, Google Norway