The only way to make it stop is by changing this setting:
- Right-click the Start Menu
- Choose Properties
- Click "Customize..."
- Scroll down and look for "Search other files and libraries" (it has three radio buttons)
- Choose "Don't search"
- Click OK
- Click OK
The only problem with this is you will also no longer be able to use the Start Menu search to pull up individual files and documents.
This is the extent of my knowledge. I'm hopeful that there's a way to do something with the e-mails themselves (or the e-mail program) to exclude it from these search results.