We got an alert that smtp went down on a customers Windows Server 2008 R2 VM. After logging in it looked like the hard drive was full. We went ahead and loaded windirstat (http://windirstat.info/) to try to track down where the usage was. Unfortunately it didn’t register. We were able to track it down however to an older version of SmarterMail (http://www.smartertools.com/) that had a 90GB clam/tmp folder with all of it’s virus definitions. There was literally hundreds of folders that administrator couldn’t delete. After futsing a bit with it I could take ownership and then give myself full privileges and delete them, but there were literally hundreds of these things. Over night a co-worker came up with the following command to run in command prompt:
takeown /f “c:\Program Files (x86)\SmarterTools\SmarterMail\Service\Clam\tmp\*” /R

Then you can delete them at your leisure and free up all that space. It’s likely because the server was running an ancient version of SmarterMail.