If you happen to upgrade from Outlook 2007 to Outlook 2010 and lose your auto-complete email addresses, there is a solution!
Start by closing outlook.
If you’re moving computers:
On the old computer, Open up C:Users
On the new computer, Open up C:Users
Then on every computer:
Go to Start > Run and run this command: outlook.exe /importnk2
Outlook will now start and in the process import the auto-completed email addresses from that Outlook.nk2 file.
That’s it. Enjoy!