Right-Hand Side Blacklist

What Does Right-Hand Side Blacklist 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.

Techopedia Explains Right-Hand Side Blacklist

Over the years, a number of DNSBLs have become vulnerable to denial-of-service (DoS) attacks. Those responsible for the attacks have not been uncovered, but many feel that spammers have been the ones to initiate them. In 2003, A DNSBL provider named Osirusoft was forced to shut down as a result of continuous DoS attacks. This outcome is likely to be exactly what those who perpetrate attacks against DNSBLs are hoping for.


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Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…