Outlook 2010 and newer missing autocomplete addresses
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If you have changed something recently in Microsft Outlook 2010 or higher you may have noticed that the people you frequently send emails to email addresses are all gone. Here is one last hope of locating those email addresses. This will only work with Windows 7 onwards.Â
Open the Windows Explorer (you can do this by opening the "This PC" or "Computer" icon on the desktop)
In the address bar paste this %localappdata%\Microsoft\Outlook\RoamCache
NOTE: to get the the address bar you can also hold the alt key + d
Normally the file starts with the naming convention Stream_Autocomplete_0_[SOME LONG GUID NUMBERS AND LETTERS].dat. You may find multiple files with this name or similar. Search for the largest automcomplete file and copy it to your desktop.
Now search for the most recently modified autocomplete file and copy it to your desktop.
Make sure that Microsoft Outlook is closed.
Right click on the most recently modified autocomplete file and click on rename, once the file is highlighted, copy the name of the file then add the word old to the end of it.
Locate the largest autocomplete file then right click on it then click on rename, then paste the name of the file you just copied then hit enter to confirm the file to be renamed.
Relaunch Microsoft Outlook and your addresses should re-appear. Thats it.
NOTE:
Beginning with Outlook 2010, Outlook does not use the NK2 file; it stores the autocomplete cache in the mailbox or data file and caches the addresses in an autocomplete stream at C:\Users\%username%\AppData\Local\Microsoft\Outlook\RoamCache. You can type or paste %localappdata%\Microsoft\Outlook\RoamCache in the address bar of Windows Explorer then press Enter to open the folder location where the cache is stored in a file named Stream_Autocomplete_0_[long GUID].dat.
Credits to https://www.slipstick.com/outlook/email/understanding-outlooks-autocomplete-cache-nk2/ for a very helpfull guide.
Here is also a useful guide that can help to backup this information.
https://www.lifewire.com/back-up-copy-auto-complete-list-outlook-1173775
