Why can't an OST file be opened in Outlook?

Some of the common reasons for such queries are

  1. Slow internet connection
  2. Error while data synchronization of Microsoft Exchange server to the .ost file on the local machine.
  3. Accessing the same OST file by multiple users at the same time
  4. Runtime conflict of certain other programs with the Outlook application
  5. Problems with Microsoft Outlook application or faulty updates.

"Outlook OST cannot be opened"- [Solved]

If you are encountering the error saying that the.ost file cannot be opened, follow some of the solutions mentioned below.

  1. Close Outlook and Kill all the Outlook related Processes

    Steps to perform the task:

    • Close your Microsoft Outlook safely.
    • Right click the taskbar and select the "Start Task Manager"
    • Choose the "Processes" tab.
    • Look for "Communicator", "Lync", "ucmapi" or "Outlook". If you find it, right-click and click the "End Process" button.
  2. Turn off Cached Exchange Mode

    Steps to turn off Cached Exchange mode:

    • Close your Microsoft Outlook
    • Go to "Control Panel", Search for "Mail" and click the "Mail".
    • Click the "Email Accounts..." button and choose the "Email" tab.
    • Click the Exchange account, and then click Change.
    • Under Offline Settings, Uncheck the "Use Cached Exchange Mode" >> Select "Next" >> "Finish".
    • Exit, and then restart Outlook.
  3. Export OST data to PST and then import it into a new OST file

    If you have Outlook 2010 or later, you will be unable to recover the OST file using ScanOST. In case your offline Outlook Data File (.ost) has local data that is not present on the server, we recommend that you export the data to an Outlook PST file, and then you delete your offline Outlook Data File (.ost). After the data is downloaded from the Exchange server, you can import the Outlook PST file into the new offline Outlook Data File (.ost). During the import, you can exclude any duplicate data from the Outlook PST file.

    To import the Outlook PST file into the new offline Outlook Data File (.ost), follow these steps:

    • In Outlook Click the File tab, click Open, and then click Import.


    • Select Import from another program or file, and then click Next.
    • Select Outlook data file (.pst), and then click Next.


    • Click Browse, and then locate the PST file that you exported.


    • Select Do not import duplicates, and then click Next.
    • Under Select destination folder, click a folder to which you want to import the information, and then click Next.


    • Click Finish.
  4. Repair Outlook and install the latest version

    If you are using an outdated or an old version of Outlook, you may encounter such problems. Try repairing Outlook manually or install the latest version of MS Outlook.

  5. Disable Outlook Add-ins that may cause conflicts

    Certain Outlook Add-ins may cause conflicts with Outlook and prevent the OST file from opening. In order to disable the add-ins follow the steps below

    • Click on Windows Start Menu or press Ctrl +R and type outlook.exe/safe.
    • This will open Outlook in safe mode. Now click on File in MS Outlook and go to Options.
    • Under Options, click on Add-ins and make sure that the COM Add-ins are selected at the bottom.
    • Click Go and ensure that you disable/uncheck all the Add-ins.


    • Restart Outlook in the normal mode and check whether you get the error again. If there are no errors check which Add-in was causing the issue by enabling them individually and removing them.

    Other Errors of OST files

    • .ost file is in use error Outlook 2010, 2007, 2003.
    • Outlook 2010 OST file in use and cannot be accessed.
    • OST file is in use by another application.
    • Cannot display the folder the file outlook OST is in use and cannot be accessed.
    • Default outlook profile.ost is in use and cannot be accessed.
    • The file OST cannot be opened or Outlook ost file cannot be opened

If you are still facing any of the aforementioned issues, try our EdbMails OST Recovery and Conversion Tool to repair the .ost file in an instant. The software works on all corrupted or inaccessible OST files and completely recovers them.

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