Troubleshoot OST Error- “the file username.ost is in use and cannot be accessed”

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  • Published on
    April 4th, 2020
  • Updated on
    February 19, 2021
  • Read Time
    4 minutes
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Whenever Outlook is used with Exchange, then all of its mailbox items get saved on the server locally in the Outlook data files with .ost extension. This will generate errors in OST files such as “the file username.ost is in use and cannot be accessed.” This type of error mostly occurred when Outlook used with Exchange. So, to fix this error, we are explaining some of the essential steps that can be used to correct it. 

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A replica of the mailboxes that reside on the server is built on the local machine while using Microsoft Exchange with Cached Mode enabled. This replica is stored in Offline Storage Table files, which are data files with an OST extension.

OST files enable users to keep on working even when the Exchange connection gets stopped. Whenever the connection restarts, all the local mailboxes get merged with its server copy.  

Now, it’s time to know the main causes behind this error.

Causes behind “the file is in use and cannot be accessed Outlook” Error:

Outlook error “the file .ost is in use and can not be accessed” is frequently encountered when attempting to opt for the “Save and Send” facility contained inside Office applications such as Word and PowerPoint. Although the error message shows that another application uses the Outlook OST file, finding the software can be very difficult for users who don’t operate on networked machines. 

There could be several other reasons for the occurrence of the error:

  • Unavailability of synchronization between the OST file and the Exchange mailbox.
  • Many users are trying to use the same OST.
  • When the processes such as LYNC, UCMAPI.EXE, Office Communicator 2005/2007, etc. run in the background.
  • Bad Internet communication Dispute of other programs with Outlook application.

Now, after knowing the main causes of this error message, let us see some tricks to troubleshoot it. 

How to fix “the file username.ost is in use and cannot be accessed” error in Outlook 2007/2010/2013/2016/2019?

Method 1: Stop MS Outlook and Processes aligned with

Try to ensure that several Outlook instances are not running and that there is no other relevant mechanism that can trigger the OST file to be marked as “in use.” 

  1. First, close the Outlook application.
  2. Then, open the Task Manager >> choose the “Processes” tab
  3. Now, you can see some processes named as “Outlook”, “LYNC”, “Communicator”, or “UCMAPI” 
  4. Choose all of them and press the “End Task” button one by one

Method 2: Deactivate Exchange Cached Mode: 

  1. Stop Outlook and open Control Panel
  2. Now, go to Mail >> Email Accounts >> Email
  3. Then choose your email-id and hit on the “Change” button
  4. Untick the “Use Cached Exchange Mode”
  5. Press the Next button
  6. Tap on Finish.

Method 3: Deactivate Outlook Add-ins:

  1. Search the shortcut icon for Outlook.
  2. Hit and hold the CTRL key and double-click the application shortcut.
  3. Then a window appears asking if you want to start the application in Safe Mode, press ‘Yes’.

Method 4: Fix OST file in MS Outlook, using ScanOST.exe:

  1. Leave Outlook, and browse to the Outlook installation directory on your device. Browse to the ScanOST.exe file in that directory, and double-click to start it.
  2. The program will prompt you to choose an OST file for repair. Select the OST file by browsing. If you are unfamiliar of its precise location, locate it in the Run dialog by typing the following:
    1. “%LOCALAPPDATA%\Microsoft\Outlook\”
  3. Pick the correct mailbox or profile name and other options when prompted.
  4. Choose “Repair Errors” and then press “Begin scan” to automatically test and delete OST file discrepancies

These manual steps will help you to repair OST files so that the “the file is in use and cannot be accessed Outlook” error will automatically get fixed. But it has some downsides that you may face like complexities, lengthy process, low speed, consume more time, etc. So, to protect yourself from these drawbacks, you can choose the below alternate solution. 

Alternate Solution: OST Recovery Software

OST Recovery program effectively repairs the inaccessible or damaged Exchange Outlook data files without any data loss. This tool developed by an advanced algorithm to quickly repair OST files so that any error related to them gets automatically fixed. You can use this recommended utility for better and instant results without any issues. 


All about “the file username.ost is in use and cannot be accessed” error has been explained in this guide including about the error, causes, and manual steps. The limitations of the given manual steps also provided here that a user may face. To avoid these limitations, an alternative way is given that helps to fix the error quickly. Hope you get some useful information through this guide.  

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