This is SBS 2011 (Exchange 2010), established almost 2 years ago.
About 10 users. So far only one user complaining about this problem.
The user is using a laptop running Win8.1, Office 2013. Outlook was configured using RPC over HTTP (Outlook Anywhere).
He received an email with blank content. We looked into this email from OWA, same problem. But, the email looked fine on his cell phone (iPhone). He forwarded the email to me from his iPhone. The content was intact, which contains only one simple sentence plus the sender's signature with a logo and disclaimer.
This problem has happened to this user from time to time and the emails could be from random senders.
I think, I have made SBS 2011 up to date, as I run Windows Update from server frequently.
I found the version info about Exchange 2010 from Exchange Management Console as below
Version 14.3 (Build 123.4)