Had a problem with a client who is running Outlook 2007 with Exchange 2010 on a 2008R2 terminal server: each message sent from Outlook (composed by Outlook) had a blank message body. The recipient side would see it like this, and the empty message would be stored in the Sent Items folder of Outlook. This behaviour was system-wide, meaning that each user was experiencing this problem.
After some digging around, I found this link on the internet stating it could be related to the virus scanner. My eye was particularly caught by a post of someone who was running Avast 4.8 on TS (which was identical to what the client was running). After disabling scan outbound mail the problem was fixed.
I quickly tried it out, and to the customer's joy, this indeed fixed the problem. Looks like there's a compatibility issue regarding this particular type of set up with Avast 4.8. Let's hope the new Avast Server release will be ready soon. Version 4.8 is way outdated if you ask me.