+ lists domains that do not adhere to common best practices or requirements
+ does NOT list spammers!
+ listing criteria are explained well
+ http://rfc-clueless.org/pages/listing_policy
+ return codes are explained
+ http://rfc-clueless.org/
+ usage policy is not so clear but the FAQ implies that it’s just free to use for everyone
+ http://spameatingmonkey.com/
+ lists IPs
+ lists domains
+ usage policy seems clear
+ https://spameatingmonkey.com/faq/query-limits
+ listing policy seems clear
+ https://spameatingmonkey.com/services
+ return codes documented
+ https://spameatingmonkey.com/services