Bill Manning wrote: > example.com. soa ( > stuff > ) > ns foo. > ns bar. > ; > mailhost aaaa fe80::21a:92ff:fe99:2ab1 > is what i am using today. In that case adding an MX record pointing to mailhost or not is perfectly irrelevant from an IPv4-only POV: IPv4-only users cannot reach your AAAA, therefore they better reject mails claiming to be from any@xxxxxxxxxxx at their border for obvious reasons. It also breaks the broken 1123 5.3.6(a) forwarding in more pieces, if the forwarder accepts IPv6-only and forwards it to IPv4-only, the receiver can't send DSNs or ordinary replies. Or if they can over another route that is something an 1123 5.3.6(a) forwader can't know. Consider it as one-way spam if the mail with IPv6-only addresses somehow makes it into IPv4-only land. That is broken, as you said, but unrelated to demanding an MX record for IPv6 SMTPs. Without a mandatory MX for your IPv6 SMTP if the mail reaches IPvAnything land and folks want to reply or send DSNs where required, they have to query for MX, A, and AAAA to finally find your IPv6 SMTP. For simple "if it can't receive it has no business to send" checks at the border it is also three queries. With a mandatory MX for IPv6 we simply reduce this. All "v=spf1 -all" and obscure null-MX ideas could be phased out if "no MX" means "cannot receive, must not send". We will never reach this ideal for IPv4, but *NOW* is a chance to prepare it for the time when the whole Internet is IPv6-only. Frank _______________________________________________ IETF mailing list IETF@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf