Procmail problems

Okay, here's one for the geek crowd. I'm trying to set up some spam filtering with procmail; but I can't get it to actually do anything. My ISP has spamassassin set up, and I've set it to tag all incoming spam messages with "[SPAM]" at the beginning of the subject line. I tried to set up a procmail recipie to filter anything with that tag (I'm currently set up to bounce it to a folder, which I will replace with /dev/null as soon as I'm sure it's working properly. So far it doesn't seem to do anything at all. I'm reading mail with PINE on a shell account, using IMAP. Could the fact that it's reading mail remotely with IMAP instead of locally with POP be the reason it isn't working?

Here's my current .promailrc file:

# .procmailrc
# spam filter

PATH=/usr/local/bin:/bin:/usr/bin:/usr/bin/X11:.
MAILDIR=/home/h/hardrock/mail #all mailboxes are in /mail
LOGFILE=/dev/null
SHELL=/bin/sh

# kill all messages with [SPAM] in the subject line
:0
* ^Subject:.SPAM.*
a_spam # replace with /dev/null

# kill all porn spam not already killed
# :0
# *^Subject:.SEXUALLY EXPLICIT
# /dev/null

I've also tried it with \[SPAM\], but that doesn't seem to work either.