RBL stands for Real-time Blackhole List (or Real-time Block List). Many internet organizations have gathered lists of the ip addresses for known spammers. GWAVA can utilize these 3rd party lists to block more spam. RBL lists aren't always going to be 100% accurate, however. False positive will occasionally happen, but the benefits usually outweigh the disadvantages.
SURBL stands for Spam URI Real-time Block Lists. SURBL works very much like RBL, except SURBL lists target URLs in the body of messages. SURBL tends to be highly accurate. False positives are rare.
GWAVA recommends the following two RBL services (these should already be listed in GWAVA by default): sbl-xbl.spamhaus.org and bl.spamcop.net. The default and recommended SURBL service is: multi.surbl.org.
Although there are many RBL and SURBL sites out there, some are not as reliable as others. Even the recommended services may be problematic for some customers. We recommend researching which service(s) will work best in your own work environment.
*Note: See KB article https://support.microfocus.com/kb/doc.php?id=7019852 If you encounter problems with black.uribl.com.