SpamCannibal is dead
The SpamCannibal blacklist – one that didn’t affect your email too much but which would panic users who found it on one of the “check all the blacklists!” websites – has gone away.
It was silently abandoned by the operator at some point in the past year and the domain registration has finally expired. It’s been picked up by domain squatters who, as usual, put a wildcard DNS record in for the domain causing it to list the entire internet.
Al has more details over at dnsbl.com.
If you run a blacklist, please don’t shut it down this way. Read up on the suggested practice in RFC 6471. If you just can’t cope with that consider asking people you know in the industry for help gracefully shutting it down.
Blacklist health checks
If you develop software that uses blacklists, include “health check” functionality. All relevant blacklists publish records that show they’re operating correctly. For IP based blacklists that means that they will always publish “127.0.0.2” as listed and “127.0.0.1” as not listed. You should regularly check those two IP addresses for each blacklist and if 127.0.0.1 is listed or 127.0.0.2 isn’t listed immediately disable use of that list (and notify whoever should know about it).
For IPv6 blacklists the always listed address is “::FFFF:7F00:2” and the never listed address is “::FFFF:7F00:1”. For domain-based blacklists the always listed hostname is “TEST” and the never listed hostname is “INVALID”. See RFC 5782 for more details. (And, obviously, check that the blacklists your software supports out of the box actually do implement this before turning it on).
If you use someone else’s blacklist code, ask them about their support for health checks. If your mail filter doesn’t use them you risk either suddenly having all your mail go missing (for naive blacklist based blocking) or having some fraction of wanted mail being delivered to your spam folder (for scoring based filters).