After shutting down Outlook forcefully and trying to restart it, the following error is displayed:

'Microsoft Outlook' exited without properly closing your Outlook data file. 'Microsoft Outlook' must be restarted. If this error message recurs, contact support for assistance.

Outlook then exits.


I've found that for me this occurs because Outlook crashed for some reason but the Lync 2010 client still has a handle to the .ost file. Exiting Lync completely allows Outlook to restart.

  • 10
    I had this exact problem and closing Lync fixed it.
    – jamesbtate
    Aug 23 '11 at 14:14
  • 4
    Ran into the same problem, Microsoft Communicator turned out to be the greedy file handler.
    – Dan Ling
    Jun 21 '12 at 14:20
  • Lync is such a sticky piece of crap. Somehow Sametime must have been contagious. May 4 '15 at 6:22
  • 1
    Also applies to Cisco Jabber
    – Enilorac
    Jan 18 '16 at 16:47
  • Your solution worked whereas the accepted answer just told me: (1) The handle wasn't found (2) The .ost file was in use by another program - Lync, as it turns out.
    – B H
    Mar 15 '19 at 14:14
  • Run Process Explorer and choose "Find Handle or DLL" from the Find menu.
  • Search for '.ost'. This will display all open handles to your Outlook data file.
  • Choose to close all handles to your .ost file
  • Start Outlook again
  • optionally - run C:\Program Files (x86)\Microsoft Office\Office14\SCANPST.EXE
  • Both this and the other answer proved to be very helpful for solving my problem.
    – Ro Yo Mi
    Sep 9 '14 at 18:54

I couldn't find any processes that had a lock on my OST. Further, closing Lync provided temporary relief since I actually need both programs running. I finally just threw in the towel and uninstalled both office 2010 and Lync 2013. I then re-installed office 365 (with Lync). After 2 days, I have yet to see this error again.

  • 1
    closing Lync provided temporary relief -- why didn't you just stop Lync, start Outlook, and then start Lync again?
    – ppeterka
    Sep 21 '16 at 7:26

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