Re: How does SMTP IPv4 and IPv6 work together

At 02:25 -0400 on 04/07/2008, Hector Santos wrote about Re: How does 
SMTP IPv4 and IPv6 work together:
> Robert A. Rosenberg wrote:
> > At 02:51 -0400 on 04/06/2008, Hector Santos wrote about Re: How 
> > does SMTP IPv4 and IPv6 work together:
> > > So this is why I believe that the only text that is necessary at this
> > > point for 2821bis is:
> > >
> > >       IPv6 senders connecting to IPv4 systems MUST be aware that IPv4
> > >       systems are ignorant of IPv6 technology and therefore SHOULD
> > >       make it possible to comply with IPv4 SMTP expectations to allow
> > >       for responses.  This implies that IPv6 senders sending mail to
> > >       IPv6 SHOULD|MUST have explicit MX records or implicit MX A
> > >       record at a minimum.
> > I have removed all of the rest of your message and left only the 
> > above. Make that SHOULD|MUST just SHOULD (and add "pointing at A 
> > and and optionally AAAA records" after the "explicit MX records" 
> > clause) and the issue is solved since only these combinations are 
> > valid:
> > Should that "sending mail to IPv6" not read "sending mail to IPv4"?
> Yes, it was a typo, corrected with your suggested changes:
>
>      IPv6 senders connecting to IPv4 systems MUST be aware that IPv4
>      systems are ignorant of IPv6 technology and therefore SHOULD
>      make it possible to comply with IPv4 SMTP expectations to allow
>      for responses.  This implies that IPv6 senders sending mail to
>      IPv4 SHOULD have explicit MX records pointing at A and
>      optionally AAAA records.
>
> I am not sure I like the last sentence since the AAAA record is 
> meaningless to IPv4 only aware SMTP nodes.
> How about:
>
>      .... This implies that IPv6 senders sending mail to
>      IPv4 SHOULD have A records resulting from explicit MX
>      queries.
How about "... pointing at A and optionally AAAA records (to allow 
the IPv6 MTA to talk to IPv6-Only MTAs)"? This preserves and explains 
the MX->AAAA section. Thus IPv4 would/could be preferred for Dual 
Stack Receivers while still supporting both IPv4-Only and IPv6-Only 
receivers.
> --
> Sincerely
>
> Hector Santos, CTO
> http://www.santronics.com
> http://santronics.blogspot.com

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