I think I could have been clearer with my message. It wasn't intended as either a criticism of the ietf list management (in fact, I use precisely the same anti-spam technique) or a request for help with configuration of my mailservers (I may not be the sharpest knife in the drawer, but usually I can figure these things out on my own). Instead, I was presenting what I thought was an interesting example of a subtle problem that can come up in ipv6 deployment. The mailserver in question uses a default redhat enterprise build (actually centos). ipv6 is either enabled by default, or just has a single check box, with no further information. The fact that ipv6 is enabled so trivially carries the implication that just enabling ipv6 won't actually damage anything. Now I know different. Just enabling ipv6 on an otherwise correctly configured and functioning ipv4 box *will* cause damage -- it will cause mail that would have been delivered to not be delivered. I could be wrong, but this strikes me as a trap that lots of people could fall into. As I mentioned, my servers actually do reject mail if they can't find a reverse dns for the senders IP. Some of those servers use ipv6; in light of all this I'm going to have to rethink that decision. For a server, the combination of enabling ipv6 and using this particular anti-spam technique may drastically increase the number of false positives -- especially as ipv6 gets more widely deployed. Best Regards Kent _______________________________________________ Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf