Recently I ran into an issue where the user complained that the autocomplete history of her Outlook 2013 get washed off every now and then. i.e. it last not more than two days, as always my first assumption was that the user is confused 🙂 but when I checkout her PC and had a look at the autocomplete streaming files, I had to agree to the user, check out the image below.

Image of multiple streaming files

Notice the numerous autocomplete streaming files created for a single outlook profile

Notice the numerous autocomplete streaming files created for a single outlook profile

Obviously after seeing this I had to agree with what user was saying and I decided to dig further.  Though I knew about Nk2 to streaming files and in the middle vaguely also remember Suggested Contacts but the picture wasn’t very clear.  Upon digging around I found lots of scattered but very useful information, so I decided to put it on a single page, Hence the article 🙂 .

OK, Lets begin with some basic questions like What is AutoComplete History ?

Remember, in Outlook (any version) when you are type email address of someone under To/CC/BCC, a list of suggestions start appearing. This list is called as Autocomplete history and is build with the email address with which you communicate via outlook. So if you are sending an email to someone for the first time its email address will not come up as suggestion but from the next time it should.

This autocomplete information is stored in a file, in fact its different kind of files with different version of Outlooks

NK2 Cache:

NK2 file was used with Outlook 2007 and prior versions of outlook. So every outlook profile on a PC (yes, you can have more than one outlook profile on a PC) used to have its own NK2 file. Suppose there are two outlook profile on the PC namely Work and Home, Then two NK2 cache file will be created with named Work.Nk2 and Home.Nk2. 

Migrating NK2 Cache to new profile: Its very simple, You just have to rename the file as the new profile name. Say for example I have replaced my earlier profile named “Work” with a new profile called “Office365” (just a name) , so I will simply go to Nk2 file location and rename the work.nk2 to Office365.nk2.

Default NK2 Location:

WinXP/Windows 2003 and before: C:\Documents and Settings[User Profile]\Application Data\Microsoft\Outlook

Vista/Windows 7/onwards: C:\Users[User Profile]\AppData\Roaming\Microsoft\Outlook

Nk2 file for an Outlook profile Named "Outlook"

Nk2 file for an Outlook profile Named “Outlook”

Autocomplete Streaming File:

Outlook 2010 onwards the NK2 file is replaced with a Autocomplete streaming file with .DAT extension. Again there is supposed to be one streaming file per Outlook profile. Naming convention of streaming file is weirdly long alphanumeric number with AutoComplete in middle and it has a .Dat extension.

PS: Interesting Fact about Autocomplete file, Its updated when you exit of outlook. So for any reason if your outlook doesn’t exit cleanly or crashes for any reason then do not expect the people you emailed during current outlook session to show up next time in autocomplete history.

Migrating AutoComplete file: If you have an existing autocomplete streaming file which you want to migrate to another profile, you just have to rename this file as the existing autocomplete file for that profile and obviously either delete or rename the existing autocomplete file.

Migration from NK2 to Autocomplete:  It’s quite possible that you are upgrading or migrating from an earlier version of Outlook to Outlook 2010 or 2013 and you want to move your NK2 file cache along. Well the process is not too bad.

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

  1. Make sure that the .nk2 file is in the following folder:

    Note The .nk2 file must have the same name as your current Outlook 2013 profile. By default, the profile name is “Outlook.” To check the profile name, follow these steps:

    1. Click Start, and then click Control Panel.
    2. Double-click Mail.
    3. In the Mail Setup dialog box, click Show Profiles.
  2. Click Start, and then click Run.
  3. In the Open box, type outlook.exe /importnk2, and then click OK. This should import the .nk2 file into the Outlook 2013 profile.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.

Note The .nk2 file is renamed with a .old file name extension on the first start of Outlook 2013. Therefore, if you try to re-import the .nk2 file, remove the .old file name extension.

Suggested Contacts

The problem with NK2 cache file was that it is Outlook Profile specific which means computer specific and is also prone to corruption and usually not backed up as it’s on a user PC.  So to resolve these concerns MS decided to incorporate something which is stored on Exchange Server (inside the Mailbox) and they built suggested contacts.  It’s a feature which lived and died with Outlook 2010. 

Its nothing but an additional Contact folder under your contacts in Outlook 2010, What makes this folder special is that, it creates the new contacts by itself, so if you send an email to someone who is not already in your contact list then a new contact will be created for it under suggested contacts. This way it doesn’t pollute your precious contacts folder with unnecessary contacts and also save the contact in case you forgot to save it and the best feature that the suggested contact folder will be available and synced on all the PC’s where you have your Outlook profile.

What Happens to Suggested contacts in outlook 2013 ?

Well if you migrated an existing profile from Outlook 2010 then for sure the suggested contact folder will be migrated to the new outlook 2013 profile, but it’s migrated as just another contact folder, do not expect it to create the suggested contacts for you.  However if you created a brand new profile with Outlook 2013 then you will not see this folder any more.

Why MS Gave up Suggested Contacts ?

It was to remove confusion of suggested contacts with Autocomplete feature, Also to ensure the hub view don’t get jumbled with unnecessary contacts.

Can I re-enable suggested contacts in Outlook 2013 ?

Nope, there is no built-in feature for it left any more, However you do have an option to use some third-party add-ins for it like Add Email Address by Sperry Software and Add Contacts by MAPILab.

With the introduction and know how of Nk2,Autocomplete and suggested Contacts, I would conclude the Part 1 of this two-part series.I hope this article was able to clear some doubts over about the never-ending confusion between these three components.

In Part 2 of this series we will actually talk about various Autocomplete issues and how to troubleshoot them, I will try to publish that asap.

Update: Part 2 Published : Troubleshooting Outlook Autocomplete issues

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An automobile enthusiast at heart and computer geek by profession, started my Career with MS in 2005.Left Jobs and started Pledge Technologies (the parent company to Grishbi) back in 2009.We have been providing IT consulting to various Small and Medium businesses across US and UK since then.Our company specialises in Microsoft Server technologies like AD, Exchange, the rest and with numerous Office 365 migrations under our belt, we quite an expert with that too. Whatever we learn in our day to day life, we share it back on Grishbi as a Thank for all the love and support our customers have given us.
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