A couple more cents on this topic... If the problem is blowing DNS caches, then one solution is to query only authoritative name servers.
Spamhaus, for example, permits 300,000 free queries per day. I bet many small sites will be under this limit even if they query Spamhaus directly with no caching. For larger sites, you rsync to your own authoritative server. Again, no caching. This will put a larger load on DNS[BW]Ls, but I think it's manageable. After all, the total volume of DNS[BW]L queries from mail servers even without caching is probably very much less than the total volume of queries that go to the root name servers and they seem to cope. (I don't mean to discount the massive job of running the root name servers. It just means that people running DNS[BW]Ls will have to be prepared to make a significant infrastructure investment. It also means that fewer people will be able to set up lists on a whim and there might be fewer free lists. Those might be Good Things if list quality improves.) Regards, David.
