The steps below can be used to prevent Exim from attaching the original message to bounce back emails.
1. Login to WHM as the root user
2. Navigate to: Home »Service Configuration »Exim Configuration Manager
3. Click on the Advanced Editor tab
4. Scroll down and look for the large blue button that says "Add additional configuration setting"
5. Click that button
6. In the new text box type: bounce_return_body
7. Set the option to: false
8. Scroll to the very bottom and click the blue button that says "Save"