Derek J. Balling writes:
On Apr 2, 2008, at 7:11 AM, Arnt Gulbrandsen wrote:
- if there is no MX record and no A, but there is an AAAA, then
the sending host MAY synthesise an MX
I think this verbiage is (IMHO) horrible. It makes an "AAAA-only" mail
server completely unreliable, as you can never know for certain if a
sending host will choose to talk to you or not.
You don't know that anyway. All the deployed MTAs that implement the
algorithm from RFC 2821 page 60 won't talk to you.
In practice an IPv6-only mail server has to have incoming and outgoing
dual-stack relays in order to talk to all the deployed IPv4-only MTAs.
That ambiguity-of-behavior is a bad idea (again, IMHO).
You can't force deployed IPv4 MTAs to see the AAAAs, so this pain is
unavoidable.
Arnt