As the Internet deployment of IPv6 goes forward, folks are starting to collect info on the deployment of junk email over IPv6. Here are
some stats from RIPE on the subject.
Their study is not particularly rigorous, in particular they have spam blocking in place on IPv4 that is not present for IPv6 (see their section on Methodology.) Their comment about DNSBLs is a concern. They are right in that DNSBLs are controversial, but some are more controversial than others, and sometimes the manner of usage is what is controversial - direct blocking at connect time is a very different thing from Spam Assassin scoring, and some DNSBLs are really bad for the former, but fine for the latter. They don't actually say what they are doing, they just indicate that they are using some unspecified DNSBLs in some unspecified manner. Another issue is that they don't really indicate which spam control measures are turned on for IPv6 vs IPv4; as far as I know there aren't any significant IPv6 DNSBLs yet (one clear difference between their IPv4 and IPv6 data), but I'd like to know if they have their greylisting turned on for v6?
Finally, I'd like to know how they can refuse connections to MTAs when the target address does not exist. A receiver has no idea what the recipient address will be when the initial connection is requested.
