Dann,
You can quickly block a sender within the SmarterMail web interface by right clicking the message, selecting Actions -> Blocked sender. This will add an entry to an internal blocked senders list content filter, by default this outright deletes the messages when they are from a blocked sender. Your end users can modify this to send to a junk e-mail folder, and a variety of other actions.
You can also leverage the bayesian filtering spam check that learns based on when your users flag messages as spam\not spam.