Barbarians at the Gate
As many of you have already noticed, we've been testing a new anti-spam system over the past few weeks. The system, Intelligent Host Analysis (IHA), was developed in-house and has been shown to eliminate half the spam destined to c4.net servers. We expect to be able to refine this system to get even better results over time.
IHA works in conjunction with the anti-spam system deployed last summer. As most of our customers are aware by now, the existing system blocks spam on a per mailbox basis. It does so based on the content of the message. It's a distributed, collaborative system contributed to by ISPs from around the world.
IHA capitalizes on the work done by the existing system. It determines the sources of spam in real time and cuts them off mid-attack as they are barraging our customers with unsolicited bulk e-mail. This provides server wide protection: unlike our existing system, it is not configurable on a per mailbox basis.
It's also important to note that c4.net's mail server never receives the message. Instead, the message is returned to the sender with an appropriate error message. Of course, as anyone who has ever tried to reply to a piece of spam knows, the original sender has been falsified more times than not.
Hosts which have attacked our servers are blocked only for a few days at a time. This ensures that, should a spammer compromise an otherwise legitimate mail server, that mail server will not be blocked for longer than is necessary to protect our customers.
This system will not eliminate all of your spam. That is not its purpose. It simply protects our servers from attacks, attacks which consume system resources. Those system resources are better utilized delivering legitimate mail. The beneficial side effect, however, is that IHA cuts spam dramatically.
As of this writing, the new system has blocked over 115,000 such attacks in the past week alone. We are now deploying the system throughout the rest of our network. Customers who have not experienced large drops in the amount of spam they receive should within in the next couple days.