Significance of .NK2 files in Outlook?

In Outlook, when user starts to type any name in the edit box or other fields like To, Cc, Bcc etc then, outlook recommends a list of names to user named as “.nK2 file”.

About .nK2 file:

This file is normally hidden in Outlook & comes under miscellaneous file category.

File location depends on the operating system used by user:-

In Windows7: drive: \Users\<user>\AppData\Roaming\Microsoft\Outlook

In Windows Vista: drive: \Users\<user>\AppData\Roaming\Microsoft\Outlook

In Windows XP: \Documents and Settings\<user>\Application Data\Microsoft\Outlook

 Nickname cache is stored in the user “profilename.nk2” file. Here, note down one thing that the profile name used is the name of user's outlook profile name. When user runs Outlook 2013 application for first time, nickname cache is imported in the form of a hidden message in user's default message store. In case, if user is using outlook account with Microsoft Exchange account then user's nickname cache is imported in the Exchange mailbox.

Remember that after ending of “profilename.nk2” file import process; “profilename.nK2” must be renamed to “profilename.nk2.old” because when user will run outlook application second time, user's nickname cache is not imported.

Outlook 2013 does not use .nk2 file for maintenance of nickname cache, its default message store is the only location for nickname cache & all the updates done in the nickname cache. In case of multiple Outlook profiles, every outlook profile is merged in to new Outlook 2013 nick name cache on first start of outlook by using that multiple profile. After merging of profiles, there is also need for renaming them from “one .nk2” file to “.nk2.old”. When user upgrades from old version of outlook to newer version i.e. Outlook 2013, then he also needs to import .nK2 files manually as they are not imported automatically.

Steps to import old.nK2 files from your previous Outlook account to new Outlook 2013

The .nk2 file folder location i.e. %appdata%\Microsoft\Outlook

Note: The .nk2 file must have the same name as your current Outlook 2013 profile. By default, the profile name is "Outlook."

1. Check the profile name by following these simple steps:
2. Click Start & hit on control panel.
   
   
   
   
   
   
   
   Now, double-click on Mail.
   
   
   
   
   
   
   
   After clicking, a “Mail Setup dialog box” appears
   
   
   
   
   
   Now, click on Show Profiles.
   
   
   
   
   
   Again tap on Start & Run.
   
   
   
   
   
   Enter following text: - outlook.exe /importnk2 & Hit OK.  
   
   
   
   
   
   
   
   After the Import process is complete, hit on OK.
   
   
   
   
   
   Note After you import the .nk2 file, the contents of the file are merged into the existing nickname cache that is currently stored in your mailbox. Also remember that the nk2 file is renamed with an .old file name extension when you start Outlook 2013 first time.
   
   
   
   
   Now, user can easily import old list of names from old computer to new computer as well as from prior version of outlook to new version of outlook.