Expired domain led to SpamCannibal's blacklist eating the whole world

The domain of the little-used SpamCannibal DNS blacklist had expired, resulting in it effectively listing every single IP address.
The first line of defence in many a spam filter is to query one or more DNS blacklists to see if the sender's IP address (and sometimes their domain) is listed as a known spammer.… https://www.virusbulletin.com/blog/2018/05/expired-domain-led-spamcannibal-blacklisting-whole-world/