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.nk2 file extension

.nk2
Microsoft Outlook NicKname data file.

This is also known as an autocomplete name list. It is a binary file used by Microsoft Outlook that contains auto-complete information, this is the information used by Outlook that lets it suggest the full email address when only part of the email address has been entered.

The .nk2 file is a hidden file. Its location varies according to the version of Windows:

Windows Version Location
Windows NT C:\WinNT\Profiles\<username>\
Windows 2000 C:\Documents and Settings\<Username>\Application Data\Microsoft\Outlook
XP
Vista + C\Users\<username>\AppData\Roaming\Microsoft\Outlook

.nk2 files were used in Outlook up to and including Outlook 2007. With Outlook 2010 .nk2 files are no longer used.

For more information see:

Can you add to this? Do you know of any applications not already listed which will work with .nk2 files, view .nk2 files or open .nk2 files? Are you able to contribute any additional reference information or file format information about .nk2 files or have you spotted any errors or omissions? If so please let us know by emailing us at feedback@cryer.co.uk - Thank you.