Outlook 2010 stopped retaining address autocomplete data

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I know that this has been asked before and I apologize in advance for opening up the topic again. None of the answers I've found have brought much clarity to the issue.

My problem is simply that, for a certain user (who of course happens to be the executive director), Outlook 2010 no longer retains address autocomplete information. It used to work but doesn't anymore. And naturally, he really likes this feature and we look really stupid for not being able to get it working for him again. He is a standard domain user on a Windows 2008R2 domain, and we are running Exchange 2010 SP1.

I understand that Outlook 2010 no longer uses .nk2 files, but rather stores the data in some hidden " thing" in the user's mailbox on the server. I've read that this " thing" is either a hidden file, a hidden folder or a hidden message. I have no idea which, nor how or even if it is possible to examine it. I've also read that data is read from this hidden mailbox " thing" on Outlook startup, into the local AppData " Stream_Autocomplete_blahblahblah.dat" file, and that as new entries are added they somehow get saved back to the hidden server " thing" as well as the new Suggested Contacts folder. Beyond that, the exact details to me are pure voodoo and I have not found documentation of how it all really works.

We've tried creating a new mail profile for him on his own machine. We've tried creating mail profiles for him on other machines. Settings in Outlook have been double and triple checked. In every case, autocomplete data is retained for the duration of a single Outlook session but the size of the local " Stream_Autocomplete_blahblahblah.dat" file remains zero bytes. After Outlook restarts, the accumulated autocomplete data is lost. Other users with Outlook 2010 don't have the issue.

Anyone have any ideas, or at least sharing the pain? I really don't want to rebuild his mailbox from scratch just for this, but that is kind of looking like the next step. Thanks alot.

Sembee [MVP]

It is a folder, called " Suggested Contacts" . It isn't hidden at all. If you choose the Folder View you will be able to see it.

Cached mode? If so I would say the information isn't being sent back to the server for sync.

Does the problem follow the user to another machine?



Simon, thank you for your response. Yes I am aware of the Suggested Contacts folder and how to view its contents. There seems to be some ambiguity among various sources I've searched, whether Suggested Contacts and the autocomplete cache are one in the same, or whether autocomplete is a separate, hidden mechanism that draws from Suggested Contacts. I've seen it described both ways.

For the user in question, Suggested Contacts is populated with entries. Ctrl+K name lookup works and will return matching entries from Suggested Contacts, just not autocomplete. New entries continue to be added to Suggested Contacts. The problem follows the user to other machines with independently configured mail profiles, both in cached mode and live mode. Autocomplete works fine for other users running Outlook 2010, so it is not system-wide.

It's just a weird thing. Thanks again for giving it some brain cycles.


Hi cyborganic,

Is there any chance the user disable the Autocomplete in Outlook 2010?

File->Options->Mail->Send messages->Use Auto-Complete List to suggest names....

Frank Wang


Hi Frank, no sorry, that isn't it. I've double-checked that the option is enabled in Outlook 2010.

My hunch now is that the mechanism that synchronizes between Suggested Contacts and the Stream Autocomplete file is somehow broken for this user. I'm going to try using the mailbox import and export tools to bring the user's mailbox contents into a new account to find out if the problem follows. Will report back.


A solution to this issue has been reached. It all revolves around the Stream_Autocomplete file. We renamed the existing, zero-byte file that would not update with new entries, then copied a different Stream_Autocomplete file with valid data to the location and renamed it with the same guid-ending that the zero-byte file had. Upon restarting Outlook 2010, we tested adding new entries by composing and sending dummy messages. These new auto-complete entries then persisted across Outlook restarts.

Details of the behavior of this mechanism as we observed it are as follows:

When new contacts are encountered by composing and sending a message, they are added to both Suggested Contacts and the Stream_Autocomplete data file. While Suggested Contacts are updated immediately, the Stream_Autocomplete file is not updated until Outlook exits. This data must then also be copied to the mysterious " hidden location" in the user's mailbox on the server, because the Stream_Autocomplete data file updates itself automatically when the same user logs on to a different machine and mail profile, presumably from the server copy.

I can say with some conviction, after observing changes in the file size of Stream_Autocomplete and the behavior of the mechanism under different circumstances, that there is no link between Suggested Contacts and Stream_Autocomplete other than when a new contact is first encountered by sending a message and then added to both locations. If a single entry is deleted from the autocomplete cache, the same entry (if it exists) is not deleted from Suggested Contacts, and vice-versa. Furthermore, clicking Empty Auto-Complete List in Outlook Mail Options completely deletes the Stream_Autocomplete file, while Suggested Contacts remains intact. If the option to Use Auto-Complete List is still enabled, a brand new Stream_Autocomplete data file is generated the next time Outlook exits, with a different guid ending than the one that was deleted. In retrospect it is quite possible that simply emptying the auto-complete list might have solved our original issue, since it generates a fresh new Stream_Autocomplete data file.

In conclusion, it's my opinion that Suggested Contacts is being erroneously depicted as one in the same as the auto-complete cache in many articles, blogs and forums describing the way the new mechaism works in Outlook 2010. In our observation, Suggested Contacts is NOT the mailbox storage location for the auto-complete cache, nor is it any kind of " window" into the cache. Entries exist in both places only because they are initially added to both by composing a message to a new, unknown contact. After that, entries can be independently deleted from either place and there is no further synchronization between them. Therefore, any issues with auto-complete not working in Outlook 2010 need to focus on what's going on with the Stream_Autocomplete data file, not Suggested Contacts.


So here's a twist...
I have the same " autocomplete not saving/sticking after outlook is closed" problem on two machines but only half of the problem. Both machines can remove pre-existing autocomplete entries using the little " x" next to the suggestion and the removal sticks when outlook is closed. (You can actually watch the Stream_Autocomplete file decrease in size when outlook is closed.) However, any newly resolved autocomplete address entries don't save when outlook is closed (The Stream_Autocomplete file does not change.). Neither computer has any problems at all resolving names from contacts or the GAB and both have autocomplete enabled. If I delete or rename the Stream_Autocomplete file, the next time Outlook is opened a new one is generated (I'm assuming populated from exchange?) with any removed entries still removed.
Computer 1 is Win 7 x64 / Clean install of Office 2010 fully updated / ForFront CS / exchange setup (cached) / iTunes NOT installed.
Computer 2 is Win 7 x64 / Upgrade install of Office 2010 from 2007, fully updated / ForFront CS / exchange setup (non-cached) / iTunes installed.
I've tried turning autocomplete on/off, clearing the autocomplete cache, uninstalling/reinstalling office, renaming/deleting the Stream_Autocomplete.dat file, disabling/re-enabling add-ins, uninstalling office updates. Nothing has changed the behavior at all. Both of these computers appear to have worked at some point but then stopped working.
So, in short, they can add and remove autocomplete entries all day long but when outlook is closed, removed entries stick but new entries don't. What gives? If outlook can remove existing autocomplete entries, why then can it not add new entries?
Thanks in advance for any suggestions!
P.S. Exchange server is 2k7.


I have users experiencing the exact same problems mentioned above.

Auto-complete only works from session to session.

The problem seems to follow the user from computer to computer.

We used NK2edit to add their suggested contacts to the cache file and that has kick started it working again.


I was able to get the autocomplete to work for a one of my users having this issue

Moved all the files from AppData/Local and AppData/Roaming to the desktop

Created new profile in Mail Control Panel

Once Outlook started, autocomplete was pulling names, even though this was the first use of this profile.
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