At 16:11 +0200 on 03/31/2008, Frank Ellermann wrote about Re: Minor
is. It's not a pardigm change:
No matter what 2821bis will say, when IPv6 enters the picture
they need to talk. The mail guy in an IPvX network will want
mail from non-IPvX networks.
Frank
So if you are a IPv6 SMTP MTA document this fact with a MX. If you
are IPv6 but NOT an SMTP MTA document this fact either with an "MX ."
or better with the absence of an MX for that FQDN.
IOW: If a FQDN has no MX, there should NOT be an attempt to find a
MTA Server for that FQDN by doing an AAAA fallback (but doing a
fall-back to an A is acceptable for historic reasons). Failure to
find an MX or an A for a FQDN should act as it does at present (IOW:
In the absence of an MX do NOT assume that an AAAA might represent a
MTA). Saying NO AAAA Fall-Back is the only way to avoid the problems
that A Fall-Back causes since there is no VALID need for AAAA
fall-back in the absence of an MX unlike the situation prior to the
creation of the MX record type that necessitated doing A Fall-Back
(since prior to the MX, the A WAS the way to find a MTA).