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:
1) MX with a IPv4 and IPv6 FQDN listed on the RHS (ie: After
resolving the IN records there should be at least one A record and
one AAAA record). This allows use of IPv4 to send to IPv4 MTAs and
use of either IPv4 or IPv6 to send to a IPv6 MTA (IPv4 only when Dual
2) MX with a IPv4 FQDN listed on the RHS (forces all incoming
traffic to be IPv4).
3) No MX but at least one A for the FQDN.
Should that "sending mail to IPv6" not read "sending mail to IPv4"?