Re: IPV6: Where are we? (SMTP)

At 22:17 -0400 on 04/06/2008, Hector Santos wrote about IPV6: Where 
are we? (SMTP):
> Why has this not been discussed as an alternative to AAAA?  It would 
> seem to me that A6 which has type value of 38 is a reasonable item 
> to be discussed  if we also going to discussed lookups for AAAA 
> records.
I seem to have the impression that the A6 version was depreciated in 
favor of the AAAA method due to AAAA being straight forward (it is 
just the IPv6 version of the A) while A6 was VERY complex to define 
(as DNS records) and implement (in code and resolvers). They were two 
different ways of defining IPv6 addresses and in the head-to-head 
competition AAAA won.
As to the Implicate MX question, I think we should take the 
conservative stance that direct AAAA references should be banned 
RIGHT NOW with this a possible relaxation of this restriction to be 
addressed at a later date via an RFC on this issue.
IOW:

IPv4-Only MTA FQDNs as at present - Optional (but suggested) MX with 
A-Fallback in the absence of the MX.
IPv6 MTA FQDNs ONLY via MX (with a recommendation that there be IPv4 
MTAs which MUST be listed in the MX [since the existence of the MX 
precludes A-Fallback]).
By INITIALLY saying "No AAAA-Fallback" we can address the issue later 
while allowing it NOW will prevent us from banning/depreciating it in 
the future (as we can see with trying to depreciate A-Fallback). IMO 
there is no VALID excuse for allowing AAAA-Fallback except for the 
"We Allow A-Fallback so we should allow AAAA-Fallback" claim. I see 
the existence of A-Fallback support as an invalid issue to avoid 
justifying the need to not require the use of MX.