How RBL and SURBL work

  • 7019722
  • 13-Feb-2008
  • 07-Aug-2017


Any version of GWAVA


How does a RBL or SURBL lookup work?



RBL/SURBL use DNS lookups to check against their blacklists. 

To understand how this process works we need to first understand how normal DNS works. For example, if I type in my web browser, the browser then does a DNS lookup to find the IP address for Once I have the IP address my browser can access the resources for the web page. Think of a DNS server as a phone book, it ties names to internet addresses.

RBL/SURBL works much the same way with a few exceptions.  If the uri '' appears in an email, GWAVA contacts their DNS server and asks it to do a lookup on '' (notice the surbl server attached on to the domain).  The DNS server will in the end contact and ask if it recognizes that domain. will return a simple, yes I recognize that domain (meaning block it, because it is on my blacklist), or no I don't recognize that address (meaning that domain is not blacklisted). DNS is merely the method used to check their blacklists.


Additional Information

This article was originally published in the GWAVA knowledgebase as article ID 195.