Outlook 2010 Auto-complete email addresses

How To Disable the Outlook 2010 Auto-Complete and Clear the Auto-Complete Cache

1. In Outlook 2010, Click the File menu and Select Options.

2. In the Outlook Options window Click the Mail tab.

3. Scroll down roughly halfway until you see Send messages. Uncheck the Use Auto-Complete List to suggest names when typing in the To, Cc, and Bcc lines box.
Optional Step: To clear out the Auto-Complete list, simply Click the Empty Auto-Complete List button.   No .NK2 file, that exists in Outlook 2003 / Outlook 2007.

4. You’ll see a confirmation window about clearing the Auto-Complete list, Click Yes.

Now Outlook Auto-Complete should be completely disabled and any history that was in the Auto-Complete list should be completely erased (if you clicked the clear auto complete button).

From
http://www.groovypost.com/howto/microsoft/disable-clear-outlook-2010-auto-complete-cache/