You can disable the Auto-Complete and/or Empty the Auto_complete cache in the send options in Outlook. Optionally, you can Empty the Auto-Complete cache.
- In Outlook 2010, Click the File menu and Select Options.
2. In the Outlook Options window Click the Mail tab:
3. Scroll down to the Send messages group. If wanting to disable Auto-Complete, simply Uncheck the Use Auto-Complete List to suggest names when typing in the To, Cc, and Bcc lines box.
To clear out the Auto-Complete list, simply Click the Empty Auto-Complete List button. Previous to Outlook 2010 this step was completed by completing the .NK2 file.