You can enable spam box from the SpamAssassin configuration screen in cpanel, and regularly check the spam box for any false positives. You can clear (empty) that spambox from the cpanel if it only gets spam. You will need to regularly clear the spambox or it can fill up your hosting space.
Filter Spam Marked Emails
Login to your cpanel, go to Mail and then Email Filter screen. Create a filter rule like this:
Select “Any header” that “contains” the string “X-Spam-Level: *****” (without quotes)
The result is this:
$message_headers contains “X-Spam-Level: *****”
Each * represents spam assassin score. 5 is a default value for spam assassin to consider that email a spam.
Note: In the new cpanel release coming up soon, the headers may change. So please check the headers of a spam marked message and create the filter from your control panel appropriately.