return codes
not documented, probably only boolean
http://rbldata.interserver.net/
- may be dead: http://www.blalert.com/dnsbl/rbl.interserver.net
+ listing policy more or less clear
+ usage policy not given but since usage is explained it’s probably free for all
+ return codes seem to be binary, i.e. either listed or not
+ lists IPs
+ lists domains/URIs
http://relaytest.kundenserver.de/
http://rv-soft.info/
http://spamcannibal.org/dnsbl_check.shtml