Well, I'm not sure if it is a problem causing these files or just a clean-up issue, but sure enough we too have ActiveSync messages in our \Windows\Temp directory. In all cases they are messages FROM: the ActiveSync user, so it appears that the \Windows\Temp folder is being used when the ActiveSync client is sending an email, before it is moved to their personal Sent Items folder. The stranger part is that all of the .eml files in the \Windows\Temp directory are modified each time the ActiveSync client connects rather than when they were first sent, making me hesitant to delete them. I'm also curious if this is WAI (Working as Intended).

If the cause of the issue was fixed and the emails will not be left in the temp folder, then maybe the cleanup is not required?

 

I just emptied my temp folder and sure enough there was a lot of eml files in there.