1. Once you are logged into webmail, select Mail->Filters
 

2. Click on "Spam Filter" to edit the spam filters:
 
3. Set the Spam Level you desire - any e-mail marked Higher than this level will be filed into the Folder you choose under "Folder to receive spam" (usually INBOX/Junk or INBOX/Spam).
 
4. Let it run for a day or two - if you feel that some items filed into Spam are mails you want to receive, set the number HIGHER. If you feel that there's still Spam being left in the Inbox, set the number LOWER.

That's it folks!