What Does Right-Hand Side Blacklist (RHSBL) Mean?
A right-hand side blacklist (RHSBL) is a listing that contains the domain names of spammers, which mail servers can be programmed to reject. RHSBL functions the same way as a domain name system blacklist (DNSBL) with one important distinction: RHSBLs include domain names rather than IP addresses.
This type of blacklist gets its name due to the fact that the domain name in an email address appears to the right of the "@" sign.