We were having this same problem with email that was being sent by our Marketing director. When I took apart his email, I found a lot of extra HTML code in his email. For example: <u1:TargetScreenSize>800x600</u1:TargetScreenSize> I think he's been getting "giggy with it".
This problem only seems to occur on our instance that is running version 7.5 SP1. Interestingly, when he sends an email to our other application which is running version 7.7.1 the email seems able to parse out the message. The email opens and the following is displayed in the {Details} field in place of the "Hello" he put in the body of his message. Note, there are a few hundred spaces between the first line and the second.
Hello 0 0 1 160 914 Columbia Bank 7 2 1072 14.0 96 800x600 Normal 0 false false false EN-US JA X-NONE
0 0 1 160 914 Columbia Bank 7 2 1072 14.0 96 800x600 Normal 0 false false false EN-US JA X-NONE
Another clue was the following line that was added to the properties. Looks like this user created a boundary or Target screen size on his outgoing email messages.
Content-Type: multipart/related; boundary="_008_D08B710C1D1ABusernamedomainname_"; type="text/html"
I'd guess that this issue was resolved in a recent release. We are using Office/Outlook 2010 and Exchange 2013.