It seems Spamhaus, one of the foremost spam blacklists on the internet, is now issuing false positives when queried for IP addresses by private email servers. Recently I have seen a lot of messages being rejected by my server for being listed at zen.spamhaus.org, but running manual queries at Spamhaus as well as an independent dnsbl check tool shows me that these IP's are blacklisted exactly nowhere. Many of the emails I missed because of this were actually important. I have solved the problem for now by removing zen.spamhaus.org from my dnsbl configuration, but will need to look for at least one other such blacklist in order to keep my inbox fairly clean. Bye-bie Spamhaus. It was nice knowing you, but you fell off the bike real quick.