This service was written in natively executable code in order to allow to issue standard DNS queries directly from the operating system. This was needed because Spamhaus and many other DNSBL won't accept the reverse query coming from the PHP function gethostbyname(), and result in a timeout and eventually a site ban from their servers. Besides the slow response, the ban is not a risk you would like to run if you furnish anti-spam services.

A typical query is formed by the reverse IP plus the testing domain name, e.g. testing the IP 127.0.0.1 (localhost) at zen.spamhaus.org becomes 1.0.0.127.zen.spamhaus.org, which would return with an error since the IP is accepted for mailing (won't leave the home server).

The USpam service, fully implemented for vBulletin, but also usable for other services, queries several databases (in first place our own). This makes it more powerful, because it reflects the sum of the effort of many sites. While some sites actively intercept notoriously known spammers and prevent to run their services (tar-pit), others limit their services to collect data about them. The first approach is not legal under all aspects, while the latter is. We collect only data and leave the decision on how to react to the single site owners, thus detaching ourselves from the potential risk to become sued by a spammer.

If you wish more information about DNSBL, please read on here:

SpamCannibal

The Spamhaus Project

SORBS (Spam and Open-Relay Blocking System)