Hi, Just an observation, I don't know whether its been changed or applied recently, but we had some mails to various IETF lists soft rejected overnight due to failure of the receiving MX to perform a successful reverse DNS lookup on the IPv6 sender address. ----- Transcript of session follows ----- ... while talking to mail.ietf.org.: >>> DATA <<< 450 4.7.1 Client host rejected: cannot find your reverse hostname, [2001:630:d0:f102:21e:c9ff:fe2e:e915] <ietf@xxxxxxxx>... Deferred: 450 4.7.1 Client host rejected: cannot find your reverse hostname, [2001:630:d0:f102:21e:c9ff:fe2e:e915] <<< 554 5.5.1 Error: no valid recipients Warning: message still undelivered after 5 hours Will keep trying until message is 1 week old This was our fault, and we now have a reverse entry for the 'offending' system, but we think this problem was in effect for longer than just last night, when we first noticed the delayed mail warnings, hence we're wondering whether this is a new policy or not on the IETF lists. It's not uncommon for IPv6 servers to be multiaddressed, so mail admins will probably just need to be a wee bit more careful, and certainly try to avoid using autoconf globals on servers. In our case our server acquired an additional global autoconf address on top of its manually configured address, which it started sending from, and as this had no reverse DNS entry we encountered the Rejects. Whether such 'authentication' is still valid for IPv6 systems is of course another question... -- Tim _______________________________________________ Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf