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.


3 Answers 3


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, 2011 at 14:14
  • 4
    Ran into the same problem, Microsoft Communicator turned out to be the greedy file handler.
    – Dan Ling
    Jun 21, 2012 at 14:20
  • Lync is such a sticky piece of crap. Somehow Sametime must have been contagious. May 4, 2015 at 6:22
  • 1
    Also applies to Cisco Jabber
    – Enilorac
    Jan 18, 2016 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, 2019 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, 2014 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, 2016 at 7:26

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