I haven't tried this, but I don't think it's possible.
If you go to your domain's CPanel, and click on file manager, you can find Spam Assassin's user_prefs file in the .SpamAssassin directory.
Now if you take a look at
http://useast.spamassassin.org/doc/M...ssin_Conf.html
you 'll see the various configuration settings that you can add to user_prefs.
Unfortunately, as far as I can see, there's no option to automatically delete Spam there.
I guess you could try setting the CPanel mail filters to automatically block mail marked as spam by Spam Assassin, but I suspect the filter gets the mail before SA, so this probably won't work.
Well... at least you can filter or delete them in your e-mail client...