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Don't say we didn't warn you 
SpamAssassin itself will not delete any emails. It's only a filter which reads email in, and passes that same email out, modified in some way. If you want to delete emails, or redirect emails, you need to do it in whatever program calls SpamAssassin.
The following procmail script will delete mail with a score of 15 or higher. By moving the # (comment) mark up one line, it will save all mail with a score of 15 or higher in a separate folder rather than deleting. The general implementation then, is that mail with a score of less than 5 goes into the inbox, a client side rule triggering on "X-Spam-Status: YES" will cause mail scoring between 5 and 15 to go into a Junk Mail folder where it can regularly be checked, and mail of 15 or higher will be stored on the server or dropped on the floor.
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