What's going on here, and how do I stop it.

Hi,
        The full headers of the spam are below.  They are amazingly short.
        I've gotten 6 copies in the past 2 days.
--
  Matthew Saroff  ---------- Forwarded message ----------
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From: Rafe(_dot_)A(_dot_)Davis(_at_)kp(_dot_)org
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To: unknownMAILERDEAMON(_at_)pca(_dot_)net
Date: Thu, 16 Apr 98 19:49:58 EST
Subject: Commercial & Industrial Printing
Reply-To: Rafe(_dot_)A(_dot_)Davis(_at_)kp(_dot_)org
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STALLION GRAPHICS
--snip--