Rudy Nedved writes:
It appears that there has been a spontaneous desire for some spiffy
new goals to be overloaded onto that one, long-standing
*requirement*.
This amounts to retro-active re-design on-the-fly.
We can't escape redesigning this. IPv6 forces us to.
I still don't understand why IPv6 forces a redesign. I don't consider
an MX record in the DNS system strongly tied to a transport.
Indeed. But this isn't about the MX, it's about what to do when the
domain in question has no MX.
...
I like falling back to A only. That imposes no new requirements on
existing code or IPv4-only hosts, and it doesn't make unrealistic
presumptions about what software runs on future IPv6-only devices.
In spirit I agree.
If something is trying to deliver e-mail, they have a choice between
looking up an A or AAAA record or looking up MX records.
RFC 2821 page 60 says quite clearly that if MX records exist, they must
be used, and that an A record is used only if there aren't any MXes.
974/1123 say much the same (some details are different).
I wouldn't quite describe this as a "faling back".
I hope you understand my perspective.
I'm afraid I don't really. Sorry.
Arnt