There are many methods of catching spam emails. Some of these methods include; content filters which inspect the message content to determine if a message is junk or not, Bayesian filters that calculate the probability of a message being spam based on the history of its contents, and white/black filters, which block or allow an incoming message based on the sender's email address. Additionally, there is a filter that acts similar to a blacklist but requires less maintenance. This filter comes from an RBL server.
RBL stands for Real-time Blackhole List. This list refers to numerous services on the Internet that keeps a database of IP addresses belonging to spammers. These IP addresses include servers that misuse their service from ISPs as well as addresses from hijacked servers that send out spam messages. Before accepting an email, email servers get in contact with RBL servers to see if the IP address is in the blackhole list. RBLs are beneficial because they are maintained by third parties who take the time to build blacklists on behalf of their subscribers.
Synametrics Technologies now hosts an RBL server. SynRBL, powered by Xeams, provides free access to its DNS-Block List to effectively block from millions of host servers known to generate spam, phishing attacks and other forms of malicious messages. The list typically includes mail servers suspected of sending out or relaying spam, as well as servers that were hijacked and are sending out malicious emails.
SynRBL was created to provide an extra means of protection to reduce the junk messages landing in the user's inbox. The service monitors many emails coming into the subscriber's emails, and checks the addresses to see if they are sending out junk messages. This will make the RBL have increased accuracy in catching junk emails.
Since Synametrics Technologies collects information from thousands of installations around the world to populate data, this allow the RBL to be very effectively. This collection of data improves accuracy in determining if an IP address (or a group of addresses) is malicious or not. In addition, having Synametrics Technologies host its own RBL server allows the detection of malicious IP addresses much faster than relying on other 3rd party RBL servers.
Please visit SynRBL's website for more details.