What is outlook auto complete or nick name file (.NK2)

What is outlook auto complete or nick name file (.NK2)

Every time that you type an email address or name in the message window of MS-Outlook, it automatically offer you a list of users and email address that you can choose. This feature is known as 'AutoComplete' and Outlook automatically build this emails list according to user activity and save it into a file with .NK2 extension.

The location of the NK2 file of Outlook

The location of the NK2 AutoCompelete file created by Outlook might be different from one computer to another, depending on the operating system and the version of Outlook. 

Here's the rules for finding the location of your NK2 file:

For Outlook 2003/2007 with Windows 2000, Windows XP, or Windows Server 2003: 

The location of the nk2 file is C:\Documents and Settings\[User Profile]\Application Data\Microsoft\Outlook 
The name of the NK2 file is identical to the Outlook profile name, with .nk2 extension.

For Outlook 2003/2007 with Windows Vista, Windows 7, or Windows server 2008: 

The location of the nk2 file is C:\Users\[User Profile]\AppData\Roaming\Microsoft\Outlook 
The name of the NK2 file is identical to the Outlook profile name, with .nk2 extension.

For Outlook 2010/2013 with Windows Vista, Windows 7, or Windows server 2008: 

The nk2 file is located in C:\Users\[User Profile]\AppData\Local\Microsoft\Outlook\RoamCache 
The name of the NK2 file is in the following format: Stream_Autocomplete_X_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.dat The X is the file index (usually 0) and AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA is a random 16-byte key in hexadecimal format.

For Outlook 2010/2013 with Windows XP: 

The nk2 file is located in C:\Documents and Settings\[User Profile]\Local Settings\Application Data\Microsoft\Outlook\RoamCache 
The name of the NK2 file is in the following format: Stream_Autocomplete_X_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.dat The X is the file index (usually 0) and AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA is a random 16-byte key in hexadecimal format.

A common question from users

One of my email contacts has a new email address as their company changed their domain name. I have deleted and re-entered her correct email address about half a dozen times in the address book and yet my PC still thinks I am sending her emails to her old domain.com instead of her new domain.com. When I entered her name it defaults to the "olddomain.com" address even though it is nowhere to be found on my PC. I have to select her "newdomain.com" address from the address book for it to work. Has anyone experienced where Outlook is keeping this old email address info? How can I can purge it?

This is an all too common experience for many users.

Use the arrow key to select the incorrect address and press the Delete key.

You can clear the entire autocomplete file (*.NK2): in older versions you need to delete the NK2 file from your hard drive.

Outlook 2010 And Newer

Outlook 2010 and 2013 does not use the NK2 file; it stores the autocomplete cache in the mailbox or data file and caches the addresses in an autocomplete stream at C:\Users\username\AppData\Local\Microsoft\Outlook\RoamCache. You can type or paste %localappdata%\Microsoft\Outlook\RoamCache in the address bar of Windows Explorer then press Enter to open the folder location where the cache is stored.

Outlook 2010 also creates a contact for people you send mail to, as insurance if the autocomplete cache becomes corrupt. Look for these contacts in the Suggested Contacts folder. This unpopular feature was removed from Outlook 2013.

Clear the autocomplete cache using the File, Options, Mail, Empty Auto-complete list button.

You can also use the /cleanautocompletecache switch to clear the cache.

Nickname Cache Is Empty :

If the users are losing addresses of people they recently replied to (but not older addresses), it's because Outlook crashes or does not close properly and the changes are not written to the NK2 file. The existing *.NK2 shouldn't be replaced by a clean *.NK2 if this happens, but new addresses you've sent new mail to or replied to won't be saved to the file. Less used addresses are replaced by new addresses when the NK2 contains 1000 addresses in Outlook 2003 or 2000 address if using Outlook 2007.

If all addresses disappear, it means something is corrupt and Outlook is replacing the NK2 with a new, clean one.

Import Addresses From NK2:

When you upgrade from Outlook 2007 and earlier in-place and use the same profile, Outlook 2010 or 2013 should import the NK2 you used with your previous Outlook version automatically on the first run. If Outlook didn't import the NK2 automatically, or you are using a new computer and didn't think to move the NK2 file, or you made a new profile, you can import the NK2 after the first run by using the ImportNK2 switch.


To import .nk2 files into Outlook 2010 or Outlook 2013, follow these steps:

1. Make sure that the .nk2 file is in the following folder:
   %appdata%\Microsoft\Outlook
   The .nk2 file must have the same name as your current Outlook profile. (By default, the profile name is "Outlook.")
2. Press Windows Key + R to open the Run dialog.
3. In the Open box, type (or paste) outlook.exe /importnk2, and click OK to import the NK2 into your profile.

The .nk2 file is renamed with a .old file name extension on the first start of Outlook 2010. If you need to re-import the .nk2 file, remove the .old file name extension.