If you are setting up Outlook on a new PC for a user and they have a need to be able to retain the autocomplete when typing in an e-mail address...
Outlook 2003/2007 the file you will need is .nk2
Earlier than Outlook 2003 you will need to find the .nck or .nick file
How to backup the Cached Email addresses from Outlook
The file(s) you are going to need is located in the users profile directory;
•Windows 7 - C:\Users\<user>\AppData\Roaming\Microsoft\Outlook
•Windows Vista – C:\Users\<user>\Application Data\microsoft\Outlook
•Windows XP or earlier – C:\Documents & Settings\<user>\Application Data\microsoft\Outlook
Copy the file(s) and back it up to another location like a flash drive or network share.
How to restore the cached email addresses from Outlook.
Basically all you have to do is reverse the backup process.
1. Make sure that you have created the profile for the person both on the computer and in Outlook and it has been logged onto.
2. Exit out of Outlook
3. Copy the file from the flash drive/network share back to the appropriate user profile directory for Outlook.
4. Run Outlook again, create a new e-mail and begin to type an e-mail address you know they have previously used on the other PC
You should see it complete the address as on the other PC...
There is a program called “NCKCSV”. This program allows you to backup your “quick outlook contacts” and save them as a CSV file. Once you have done that you can import them into your contacts in outlook. I have not personally used this, but I have heard it works fine.