At 10:27 -0700 on 04/04/2008, Dave Crocker wrote about Re: current
usage of AAAA implicit MX?:
ps. While surveys are always useful, I'll repeat the observation
that changing the query model for SMTP is out of scope. The current
model is 1) look for MX, 2) look for address record (A and/or AAAA).
Anything that removes step 2 is a model change.
What is being talked about is NOT removing Step 2 but restricting it
to looking at A records. Looking at AAAA records in Step 2 should not
be allowed since due to the ability to use an MX record to point at
an IPv6 MTA, there is NO NEED (unlike the IPv4 case due to historical
support for locating an IPv4 MTS directly by its A record) to EVER
expect that an IPv6 MTA should/can be DIRECTLY locatable via its AAAA
record.
Even RFC 3974 talks ONLY about the use of MX records to locate IPv6 MTAs.