>As a result, it is questionable whether any IPv6 address-based reputation >system can be successful (at least those based on voluntary principles.) It can probably work for whitelisting well behaved senders, give or take the DNS cache busting issues of IPv6 per-message lookups. Since a bad guy can easily hop to a new IP for every message (offering interesting new frontiers in listwashing) I agree that it's a losing battle for blacklisting, other than blocking large ranges of hostile networks. Fortunately, the IETF as a whole is not called upon to solve this problem right now. People interested in mail reputation are welcome to drop by the spfbis WG and the discussions in appsarea about updating authentication and authentication logging RFCs.