https://www.kisarbl.or.kr/
https://www.megarbl.net/
https://www.team-cymru.org/Services/Bogons/dns.html
+ good reputation
+ lists IPs
+ does not list spammers but bogons
+ clear listing policy
+ usage policy not quite clear ATM
+ return codes documented: binary
http://mailspike.net/usage.html
reputation-based
https://puck.nether.net/or/