How to reset the nickname and the automatic completion caches in Outlook

Have you ever wondered where Outlook stores data it uses to auto-complete email addresses when you are typing in the To or Cc field?  Microsoft stores this data in a file with the extension .NK2.  The cache file is stored in each user’s profile in drive:\Documents and Settings\user name\Application Data\Microsoft\Outlook.  Note that this may be a hidden folder, so you may need to change your view settings to see the file.  The file should be named outlook profile name.nk2.
Every time you enter a new email address when composing an email that address will be added to the nk2 file so that the next time you type the name, the auto-complete feature will try to guess what you are typing and fill in the details for you.

If this nickname cache file is corrupted, Outlook may not be able to identify recipients, may offer incorrect recipients when automatically completing the email address, or may send the message to the wrong person.

Outlook 2010
Use one of the methods listed below to reset the Outlook nickname cache for Microsoft Outlook 2010.
Method 1
1. With Outlook 2010 open, click File (BackStage), and then click Options.
2. Click the Mail tab.
3. Under Send Messages, click Empty Auto-Complete List.
Outlook will generate a new nickname cache.
Method 2
1. Click Start, and then click Run.
2. Start Outlook by using the /CleanAutoCompleteCache switch.
For example: Outlook.exe /CleanAutoCompleteCache
Note If Outlook is not installed in the default location, you will need to point to the path of Outlook.exe.
Outlook will generate a new nickname cache.


Outlook 2002 through Outlook 2007
Use the steps in the following section to reset the Outlook nickname cache for Microsoft Windows XP.
1. Quit Outlook.
2. Click Start, and then click Search.
3. In the Search Companion left-side panel, click All files or folders.
4. In the All or part of the file name: box, type *.NK2.
5. In the Look In box, click to select your local hard disk.
6. Click More advanced options, click to select Search hidden files and folders check box.
7. Click Search.
8. Right-click the .NK2 file with the name of the profile that you want to reset, and then click Rename.
9. Rename the file to profilename.bak, and then press ENTER.
10. Quit Windows Explorer.
11. Restart Outlook.
Outlook will generate a new nickname cache.

Additional function you may want to perform:
Move the cache file from computer to computer.
The file is profile specific, so you need to be sure that the profile exists on both machines.  Once that is done, it’s simply a matter of copying the file from one machine to the other. 
The location of the file is in:
drive:\Documents and Settings\user name\Application Data\Microsoft\Outlook\outlook profile name.nk2
If you have a new outlook profile that is the destination for the file, just rename the file to the new profile name.  This means that you can copy the same file to multiple users, just rename the file for each profile.