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A user reported that they no longer had their usual autocomplete* functionality when typing an e-mail address in the To: bar of a new e-mail in Outlook 2010

However if they sent an e-mail to someone, that address would then appear as an AC* but I discovered only for that session. Closing and then opening Outlook would put it back into an "empty" state.

As this is Outlook 2010, it uses a .dat file which takes the form of with stream_autocomplete<guid>
The file is located here > c:\users\%username%\appdata\local\outlook\roamcache\

The file was 446Kb in size which indicated that it had data in it. First thing I did was to take a backup of the file. Then I opened it in notepad, it looked as if it contained e-mail addresses.

Outlook settings were checked and the user had the "use autocomplete" option ticked.
Closed Outlook and I sent the AC file to the recycle bin. Ran Outlook, it recreated the AC file with a different <guid> but it was the same size and contained the same data as the other file.
Autocomplete in Outlook still did not work. Closed Outlook again.
This time, I took another copy of the original AC file and then renamed it to be the same as the newest AC file, obviously deleting the other one first! Then I ran Outlook again. No change...
Turned off autocomplete in the Outlook options and closed Outlook again. Deleted all AC files except for the backup copy I originally made. Ran Outlook. No AC file created. Turned autocomplete back on and then closed Outlook. Ran it again and a new AC file was created which was the same size as the backup copy.
Still there were no entries when typing an address into the To: bar of a new e-mail. But if you sent an e-mail, that address would be remembered, but only for the duration of the session, as before.

Now I am getting slightly frustrated. Some reading I have done suggests that there could be a problem with the data within the AC file itself.
So I decide to "empty the autocomplete list" and then turn it off from the Outlook settings.

Then I ran Outlook and there was then no AC file re-generated. I re-enabled the "use autocomplete" option in Outlook and restarted the program. At which point I sent a new e-mail to an external address. This was remembered and I noted a new AC file had been created and was only 2Kb in size. Outlook was closed and run again to see if the e-mail address I had just sent to was remembered. It was! So a small success.

But there was still the issue of all the old addresses in the original AC .dat file and how to get them into the new AC .dat file.

My initial thought was to close Outlook, rename the smaller AC file with a prefix of SLIMMER (sue me!) then to take another copy of the backup of the original AC file and rename it to match the original name of the slimmer AC file. Got that?

Ran Outlook, unfortunately it ignored what I had done and created a new AC file 2Kb in size.

Did a bit more reading and saw that it might be possible to use the latest version of a utility named NK2edit to get at the data in the file and save it back out.

So after downloading and installing the utility from the programmers website www.nirsoft.net I ran it and saw that it could load .nk2 and .dat files. and show all the e-mail addresses it contains. Again I took another backup of the original .dat file and loaded this using the utility. Then I saved it out to the current AC .dat file which Outlook had last used. Don`t make the mistake I did when first trying this and have Outlook running, as N2Kedit cannot save to the current AC file while Outlook is running, because said file is locked!

Anyhow, I overwrote the file. Fired up Outlook and as if by magic, all of the users original autocomplete entries are now there.

So a good result in the end.

Here are the steps to take in order to fix the above problem.

• Take a backup of the Stream_Autocomplete<guid>.dat file located in c:\users\%username%\AppData\Local\Microsoft\Outlook\RoamCache
• In the Outlook mail options
  
  • Empty the autocomplete list
  • Turn off autocomplete
• Close Outlook
• Delete the Stream_Autocomplete<guid>.dat but retain the backup
• Run Outlook and ensure a new Stream_Autocomplete<guid>.dat is not created
• In the Outlook mail options, turn on autocomplete
• Send one e-mail to an external address and close Outlook after It has been successfully sent, this should create a new Stream_Autocomplete<guid>.dat file of around 2Kb in size
• Download and install Nk2edit from Nirsoft
• Run it and load the contents of the original, backed up Stream_Autocomplete<guid>.dat file
• Save this data out to the newer Stream_Autocomplete<guid>.dat overwriting when prompted
• Open Outlook and you should have autocomplete back to how it was