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\\AppData\Roaming\Microsoft\Outlook. Copy the file called “Outlook.nk2”
On the new computer, Open up C:\Users\\AppData\Roaming\Microsoft\Outlook. Paste the file.

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!