Be Gone!
It looks like it may be a never ending war against unwanted commercial e-mail. But my web host, pair.com, has finally gotten half-way serious about SPAM by installing SpamAssassin to filter out spam. I say half-way because there are other filters that can, after a period of time, reach a 99 percent accuracy rate, which SpamAssassin doesn't come close. I've talked about those filters before (see it here) so I won't bother recounting it.
Suffice it to say I am happy just to have something. Time will tell whether this service is useful.
For those using pair, and probably everyone else, you must first enable the filter by going to your server account and editing your mail settings. There are fairly clear instructions on how to do this by going to here. Once you have the server side setup you need to create a filter in your email client. The instructions for the common clients are here.
As the process suggests, SpamAssassin does not delete spam. What it tries to do is identify what may be spam and adds something like **JUNK** to the header. What happens to these e-mails are then up to you to decide. It is suggested that you set-up your mail client to filter on the keyword **JUNK** and automatically have them moved into a separate folder that you can check at your leisure.
Why not just automagically delete the e-mails identified as spam? Because no filter is perfect. Some e-mail that is not spam will be misidentified as such (Type I error). If you automatically deleted all such mail you would be loosing mail you actually wanted to read. Of course, if you try to avoid Type I errors, you tend to increase the probability of having Type II errors. That is, more spam could be let through the filter. As in many things in life, it is about balance.
For the first 10 e-mails I got after enabling SpamAssassin, seven were correctly identified as spam, two were correctly passed through, but one legitimate e-mail was misidentified as spam. I added the sender to the list of acceptable domains and all should be well. Depending on how many mailing lists you are on, it may take awhile to "train" the program to let through what you want.
Is it worth it to use SpamAssassin? Well, that's something only you can decide but one error in ten ain't bad. YMMV.