Tony has a post about anti-spam, specifically what the three worst cases for filitering spam.
The third worst thing: having spam get through to users. Of course, this is what we’re trying to fight, but having spam get through, although bad, isn’t the absolutely worse thing that can happen.
The second worst thing that can happen is blocking a good email. False positives are the challenge in anti-spam solutions. I would much rather have hundreds of spam messages get through than to block a single good message. But blocking a good message isn’t really the absolutely worst thing that can happen.
The worst thing: The absolutely worst thing that can happen in your anti-spam solution is to block a good email and not let anybody know about it!
I’ve been getting more and more complaints from my end-users at work in regards to junk in their inbox, and regardless of how they managed to subscribe themselves for it, it is still a problem. In my almost three years there, our policy has always been “Let the end-user be their own filter” rather than us filtering it on the server end of things. I’ve been pondering lately turning on our spam filtering service within Ipswitch, simply for logging purposes for a few weeks so I can gather some stats and not change a thing on the user end of things for now. After collecting data, I could make a judgment on whether or not something needed to be done. I probably don’t need to get too cozy with it though, as we’re planning to move our mail to a Linux box later in the year and that would just be another feature to have to implement.