“I have some good news and some bad news. The good news is that Mail’s Junk Mail filter, when properly configured, can be a reliable tool for keeping spam out of your In box. The bad news is that even if the Junk Mail filter is working as well as it possibly can, you may still see more spam than you would like. Luckily, other applications and techniques can make up for the Junk Mail filter’s deficiencies. You’ll be able to make better decisions about how to use (or supplement) the Junk Mail filter when you know what happens behind the scenes,” Joe Kissel writes for TidBITS.
“Mail’s Junk Mail filter has two modes: Training and Automatic. (You can also disable it entirely.) Exactly what happens in these two modes can confuse the uninitiated. In particular, many people wonder whether the filter continues to learn if you switch to the Automatic mode. (It does indeed, though Apple’s documentation obscures this fact.) Here are the details,” Kissel writes. “The ‘Message is junk mail’ condition sounds rather mysterious, but it means that, if true, Mail’s latent semantic analysis filter (discussed in the full article) has assigned the message a value beyond its arbitrary threshold for spam. You cannot modify this threshold, but if you later mark the message as ‘Not Junk,’ you decrease the probability that Mail will consider a similar message to be spam in the future.”
This is a must-read for users of Mac OS X Mail; it’ll help you filter the junk and understand what the heck is going on in Mail. Full article here.