Some time ago, I had a user call in with a bounceback issue. They had sent us a screenshot of the bounceback, informing us that the email became illegible when they tried to forward it to us. I called the user up, remote controlled her computer, and had her demonstrate the issue, and sure enough; when she hit forward, all text turned to chinese (or chinese-looking) characters:
After a bit of checking around, I resolved this by upgrading the user to a patched version of Office 2013 (or later). Alternatively, you can upgrade to Office 2013, and install the Hotfix 2910923, which is available from Microsoft. If upgrading to a later version of Office is not an option, the issue can be worked around by forwarding the bounceback email as an attachment by clicking “More” and then “Forward as Attachment” in the Respond area of the Outlook ribbon.