You can do this Aggressively or not. It's up to you. Aggressive SPAM filtering will remove [almost] all SPAM and every now and so often, legitimate email as well. Moderate filtering will remove most spam ald hardly ever remove legitimate email.

Moderate SPAM Filtering

This setup will:
1) Do nothing to emails with a SPAM score below 5
2) Move messages to the spambox if they have a score of between 5-15
3) Remove messages with a score of 16 or above

According to the SpamAssassin website, 99.95% of emails with a score of 15 or above are genuine spam, so we'll set it to 16 (the umber of "*" below) to be safe.

Procedure:

1) Enable SpamAssassin from cPanel Control Panel (under "Email")
2) Enable Spambox (same place)
3) Click on "Email filtering"
4) Select "Add Filter" and create a filter using "Any header" & "Contains" with the text below as the search string:
X-Spam-Level: ****************
(Note the 16 "*" 's)
5) Leave the destination as "Discard".

Hey presto. All done!

Aggressive SPAM filtering

This will move ALL mail on all accounts on a domain to one mailbox or trash them:

Procedure:

1. In Cpanel goto Mail, then click Spam Assassin.
2. Enable Spam Assassin
3. Click Configure Spam Assassin.
4. Set rewrite_subject to : *****SPAM*****
5. Go back to mail. Click on the E-mail Filtering link.
6. Click Add Filter
7. Select SpamAssassin Spam Header in the drop down box.
8. Select Subject Contains in the next drop down box.
9. In the blank box, type *****SPAM***** (must be identical text to what you entered in 4 above).
10. Under Destination, enter either:
a) An email address you want to send the spam to OR
b) Discard to trash it.
Done. All email tagged as spam will be either sent to a spam box of your choice or it will be deleted.

WARNING: DO NOT enable Spam box unless you plan on checking your spam folder (with Horde only!!. It does not work with the other webmail clients) at least once / week and clearing it out.

If you do not do this, your mailbox fills up real quick and all mail gets bounced back to the sender with a "mail could not be delivered - mailbox full" error.