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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