qmail + vpopmail + procmail

[Angelin Lalev]

Greetings,

It's been a long time since my last day as a system administrator,
but recently I needed to install a qmail server for a friend.
Although I had forgoten many things, I've managed to make
a working netqmail 1.05 + SMTP-AUTH + TLS patch +
qmail-scanner + spam-assassin + courier imap + vpopmail (mysql db)
installation, following scattered trough internet documents and
howto's.
But now my friend's clients want all mail that is tagged as spam
(in my case, prefixed with "[SPAM]" in the subject)  moved to
separate courier imap folder (for example .SPAM).
I figured out (maybe I make error here) that I need procmail
to deliver the mail to the different courier-imap folders in the Maildir.
I couldn't find on the net clear algorithm that does that. (or at least
I failed reproducing it).
Anyone could help?