Every day I get a warning message that yet another 1% of my hard drive is gone. Since I am not saving any big files like pictures or music on it, primarily only Office files, I couldn't figure out where the space was getting eaten up from.  I used WhatSize to investigate, and the hog turns out to be Outlook. 33.5 GB is for message sources.  What is "message sources"?  How can I keep this from multiplying so fast?  I only have 5% left on my hard drive.  The 2nd biggest thing on my hard drive is Application Support at 15.2 GB, so it seems that Outlook is clearly the hog.  How can I control this ravenous beast?