This functionality should be present in the last few major versions of SmarterMail. Have you checked to make sure the user has the sender listed as a blocked sender, and that SmarterMail has been configured to send Blocked Senders to the junk mail folder? I've attached a screenshot of where this needs to be set within the user's account settings:
Kyle Kerst
IT Coordinator
SmarterTools Inc.
www.smartertools.com