At 11:38 +0200 on 04/05/2008, Michael Storz wrote about Re: current
usage of AAAA implicit MX?:
> - Number of your IPv6 MTAs which must be located via AAAA (ie: Which
belong to a FQDN with no IPv6 MX).
None. And this is also true for IPv4. All of the hundreds of local MTAs in
the Munich Scientific Network (MWN) are routed via MX RRs to our MTAs or
to the MTAs of their departemental email servers. Port 25 is blocked from
the Internet to the MWN since 10 years.
Does this answer your question?
Yes. In your case, there is (as there should be) no reason to support
AAAA-Fallback in the absence of an MX record (since there are no
missing MX records).
Since you were talking about domains SENDING to you (and your MTAs
are dual stack), an interesting question is what is the MX status of
those who send to you via IPv6 - IOW: How many of the MAIL-FROM FQDNs
have no MX or A records but only AAAA? I am NOT asking you to provide
this info but only say that it is a useful metric for the
AAAA-Fallback issue.