Hi Dave, I sure understand the problem that the scarcity-based address reputation hack won’t work that well on IPv6. But the “solution”… And NIST isn’t exactly Mom and Pop’s Bait and Internet Shop. On 13 Mar 2017, at 18:21, Dave Crocker <dhc@xxxxxxxxxxxx> wrote: > > In one of the anti-abuse organizations, I've tried to point out the problems with imposing policy changes based on transport -- independent of whether the policy change is a good idea -- but to no avail. Well, to add insult to injury, this was a DEFER code, so our mail server tried for five days to deliver this; of course using IPv6 all the time. No idea whether there is code around that can react to a DEFER with a change of source address. Grüße, Carsten