:: what is RBLs
RBL is short for Realtime Blackhole List, a list of IP addresses whose owners refuse to stop the proliferation of spam. The RBL usually lists server IP addresses from ISPs whose customers are responsible for the spam and from ISPs whose servers are hijacked for spam relay. [ webopedia.org ]

:: how to enable RBLs on cPanel

:: links
+ google
+ sysadmingear