My first time configuring procmail. I really wonder what the author was smoking when he designed the syntax. I understand better the old saying : LSD and Unix both come from Berkeley. This is no coincidence.
How can someone make such a braindead syntax ? ':0:' means use a lock file when delivering. ! means forward to an address. My God.
Anyway, the good part of it is that it is very standard, fetchmail can deliver directly to procmail. And once you have set-up the basic rules, you won't touch it often. So it is more or less ok.
Now my spam is all filtered out. MMh, what a delight. Thousand thanks to bogofilter and Paul Graham.