listing policy seems to be: they received spam from an IP
usage policy: Anyone can use this RBL list [sic]
return codes: probably boolean, i.e. either listed or not
+ http://relaytest.kundenserver.de/
+ by 1und1 (now ionos?), used internally
+ https://www.blalert.com/dnsbl/relays.bl.kundenserver.de
+ no usage policy found
+ no listing policy found
+ no return code explanation found
00_E_PAID
00_E_PRIVATE
88.blacklist.zap
return codes
not documented, probably only boolean
http://rbldata.interserver.net/
- may be dead: http://www.blalert.com/dnsbl/rbl.interserver.net
- http://relaytest.kundenserver.de/
+ 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://rv-soft.info/
http://spamcannibal.org/dnsbl_check.shtml
http://spamrats.com/