Blacklists are databases with IPs or DNSNames one could want not to accept mail from. There are several different reasons one could find to do that, so there are several lists out there. Some for example of open relays, Sites ignoring RFCs, Urls referenced in Spam emails, and so on. There are several indexes of DNSRBLs out there, for example this one on RBLs on Wikipedia.
Heres a list of RBLs thats utilized by other citadel operators:
- zen.spamhaus.org (former sbl-xbl.spamhaus.org)
- blackholes.mail-abuse.org (commercial)