Answer
Reliable DNSBL servers are:
rbl.maps.vix.com:127.0.0.2 dialups.mail-abuse.org:127.0.0.3 relays.mail-abuse.org:127.0.0.2
Note: These are paid for services
Many customers report over many false positive reports using the ORBS list so we would recommend that this is not used.
Keywords:DNSBL, Black List, SPAM