Re: Registration model, 2821bis-06

--On Wednesday, April 02, 2008 11:01 AM -0700 
ned+ietf-smtp(_at_)mrochek(_dot_)com wrote:
> > Connectivity to/from AAAA-only mail servers will suck
> > terribly for many decades to come, but no 2821bis
> > wordsmithing can avoid that. Only an arrangement with a
> > dual-stack relay can improve connectivity, and that
> > practically requires an MX RR or more.
> This is certainly true for the Internet email service. But not
> all use of
> standardized email protocols (including usage on the open
> Internet) is in
> futherance of this service. It is entirely possible that at
> some point
> an alternate service offering will emerge that's IPv6-only. I
> have no idea
> how likely this is but it is not beyond the realm of
> possibility.
And, in addition and FWIW, the claim that a dual stack setup 
"practically requires" an MX setup is false, as has been pointed 
out before.   The following setup, with no MX record, is all 
that is necessary under the current 2821 standard:
  destination.example.com. IN A ...
                           IN AAAA ....

That would cause, regardless of how this argument about 
AAAA-based synthesis comes out, an implicit MX record equivalent 
to
  destination.example.com. IN MX 0 destination.example.com.
to be generated and then address selection algorithms specified 
elsewhere to be used.
If one had stronger preferences about which interface type was 
preferred, one could use MX records to specify that.  But that 
has been the case for a long time and none of these proposals or 
options changes that.
One can sensibly argue that the flexibility about address 
(actually interface) selection is too broad and could be 
tightened.  But that, too, is a major new piece of work.
And, like Ned, I'm tiring of repeating myself about this.

   john