Working with the Auto-Complete Cache

“Fire!!” “Earthquake!!” “Tornado!!” – all of these desperate screams for help pale in comparison to the shriek heard from end users after getting a new mail profile. As the words “Hey, my contacts are gone!!” come bellowing down the hall, many techies simply feel like packing up, retiring and heading for a more rewarding career – perhaps that of a trash collector or road sweeper. Truly, the world has come to en end if [insert_name_annoying_user_here]  has lost his contacts!

Or, maybe not. While it is true that there are few things that both irk and are more readily noticed than a missing auto-complete cache, the file itself is fairly easily managed. With a little bit of extra work, you will be able to avoid many of the pitfalls that plague IT administrators after a profile switch and you will also be able to help end users clean up or reset their cache completely.

Before we get going, however, it is worth noting that the auto-complete cache is simply that – a cache. As such, it has very little offered by Microsoft in terms of editing it and in Microsoft’s eyes is more of a temporary data repository rather than some sort of proper database. Don’t expect to get stellar support from Microsoft should this become corrupt – the official line is that all addresses should be kept in your address book or outlook contacts. As a matter of principle, I must admit that I too agree with this advice.

Nevertheless, users expect their cache to be manageable so let’s dive in and look at what can be done with this.

The cache itself is implemented in the form of a file that has the .NK2 extension and is named after the name of your outlook profile. By default, this name is likely going to be “outlook.nk2”, but be aware of other names. In Vista and Windows 7, you will find this located at:

“C:\ Users\UserName\AppData\Roaming\Microsoft\Outlook”   

in Windows XP     

“C:\ Documents and Settings\UserName\Application Data\Microsoft\Outlook”      

In order to see this file, you will have to ensure that you have enabled the display of hidden files and folders.  (Learn how:Show Hidden Files)


So, once you have the directory open, it is likely that you will not see an auto-complete cache in that folder. Outlook only creates this after an email is sent and Outlook is closed and re-opened, so go ahead and send a test message to yourself, or whoever you see fit. This will cause an entry to be written to the .NK2 when Outlook is closed and reopened. After doing this, ensure that Outlook remains closed as having Outlook open will put a lock on this file and prevent you from renaming it.    

Now, take not of the name of the new .NK2 file. You will have to find the previous one from the old profile, move it to the new directory and rename it to the exact name of the new .NK2 file you have created. Go ahead and rename the new one to profilename.bak. Rename the old .Nk2 file to the name of the newly created one. Finally, reopen outlook and you should have all of the old auto-complete entries available.

Now, given this information, one of the easiest ways of creating a brand new .NK2 cache should the old one be corrupt, is to simply follow the procedure above and just rename the .NK2 file.

Another useful tidbit, is that individual entries in an an auto-complete cache can be deleted by simply hovering over the entry in the drop down and pressing the delete key while it is highlighted.


In Outlook 2010, Microsoft has also added a red X with which you may delete the entry by clicking on it. You can also get a brand new cache in Outlook 2010 by using the Outlook.exe /CleanAutoCompleteCache switch. Simply cut and paste this into the run box and you will end up with a brand new cache.

If you need more extensive editing capabilities of the .NK2 cache there are several free and relatively cheap editors out there that will allow the import of entries and correction in an easy to use editor.

So don’t worry about finding a pair of overalls just yet for your new career, there really are ways of dealing with the auto-complete cache.  I hope this little tutorial helps!



  1. We have a very nice FREE Outlook NK2 Auto complete cache rebuild tool.

    I recommend only building the cache on trusted folders on sent folder, if you rebuild on Inbox you basicaly making a cache of inbound emails wich could contain alot of spam.

  2. Thank you for the sharing, we can discuss about this. I was recommended a free data recovery software named MiniTool Power Data Recovery. Have you heard about it? My friend said it was efficient and convenient.

  3. Thanks for sharing. I suggest you go to got windows 10 product key. Yesterday I purchased from their website. Every time I was surprised price and customer service. I recommend this site to many friends. Will prove my words.


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