When you start Microsoft Outlook 2010 for the first time, your nickname cache (stored in the profilename.nk2 file) is imported into a hidden message in your default message store.
Note profilename is the name of your Outlook profile.
For example, if you are using a Microsoft Exchange account, the nickname cache is imported into a hidden message in the Exchange mailbox.
Note Earlier versions of Outlook store the nickname cache .nk2 file in the following folder.
Windows XP Drive:\Documents and Settings\Username\Application Data\Microsoft\Outlook
Windows Vista and later versions Drive:\Users\Username\AppData\Roaming\Microsoft\Outlook
After the nickname cache is imported, the profilename.nk2 file is renamed to profilename.nk2.old. On the next start of Outlook, your nickname cache is not imported. Outlook 2010 does not use the .nk2 file for maintaining your nickname cache. All updates to your nickname cache in Outlook 2010 are made to the hidden message in your default message store.
Note If you have multiple Outlook profiles, the nickname cache from each profile is merged into your new Outlook 2010 nickname cache on the first start of Outlook 2010 by using that profile. Therefore, you may find more than one .nk2 file renamed to .nk2.old.
However, there may be situations where you have to import a nickname cache file after this first-run nickname cache import process has finished. For example, a colleague wants to share their nickname cache with you and you want to update your existing nickname cache with your colleague’s data.
This article discusses how to import .nk2 files into Outlook 2010.