It looks like most of them still rely on Naive Bayes applied to individual keywords, to flag messages. They fail to catch 90% of the spam, yet have a terrible "false positive" rate - as high as 5%.
Are there any companies working on customized (e.g. per email account) solutions? Are there any spam detector that
Actually, I think they are.
Ok, let's start from the beginning: they were, when spam started being unbearable approaches like Naïve Bayes labeling were very good, then of course the evil side could not stand still and used more elaborate strategies like botnets (disabling ACLs).... and so spam detection became a moving target, a cat and mouse game.
The thing is that there is one thing bad guys can't get around and that thing is the unsolicited content, which reduces the problem entropy quite a bit and so can be tackled. Or at least the guys and gals at the company that starts with a G and that provides email services are doing a very good job at it AFAIAC.
Then of course the jury is still out on what constitutes actual spam for specific individual, but then I was thinking that the people at big G have me in some specific group of users with alike sense of spam consideration... hence when one of us tags some email as bad, the rest of us benefits quickly.