What the problem is: If you do not want a user’s email application to receive a copy of email messages that the user sends from the BlackBerry® device, you can turn off synchronization for email messages that the user sends from the BlackBerry device.
What is causing said problem: —
How to Turn off Sent Item Sync for Blackberry:
1. In the BlackBerry Administration Service, on the BlackBerry solution management menu, expand User.
2. Click Manage users.
3. Search for a user account.
4. In the search results, click the name of the user account.
5. Click Edit user.
6. In the Messaging configuration section, click Default configuration.
7. On the Services tab, in the Email services settings section, in the Save copy in sent folder drop-down list, click No.
8. Click Continue to user information edit.
9. Click Save all.