The file username Ost is in use and cannot be accessed Outlook error

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The error message “The file username. ost is in use and cannot be accessed” usually means that the Outlook data file (named username. ost) is open or in use by another program, and Outlook cannot access it. Sometimes this error message also appears for users who have enabled the “Use Cached Exchange Mode” option in their Outlook account settings; this option downloads and stores Outlook emails locally in a file named username. ost so that users can access their Outlook emails offline. In this case, the error message means that Outlook is trying to access the cached file while it is in use by the user or another program.

Outlook Data File – The file C:\Users\<username>\AppData\Local\Microsoft\<username>\username.ost is in use and cannot be accessed. Close any application that is using this file, and then try again. You might need to restart your computer.

However, if your computer or Outlook crashes during the sync with the Exchange server, you may start getting the file username. ost is in use and cannot be accessed whenever you are trying to launch Outlook, which blocks the program from opening. The error occurs because of the username.ost file is still in use on your PC or corrupted due to the crash.

Having discussed the about of this Outlook error, we will cover proven methods to fix the issue and get the app back to its working condition.

Causes of the file username Ost is in use and cannot be accessed Outlook error

The file username. ost is in use and cannot be accessed Outlook errors are as follows: the known reasons that cause the error are that the file is in use by another program or that the file is corrupt.

  • Corrupt OST file.
  • Lack of Synchronization between the OST file and Exchange server.
  • Conflicting Use of the OST File.

Fix The file username Ost is in use and cannot be accessed Outlook error

Whenever the file username. Ost is in use and cannot be accessed error appears when trying to launch Outlook on your computer, you should first restart your computer. If the issue persists, then try the solutions below to fix it:

Related Article: Outlook The file username Ost is in use and cannot be accessed

  • Restart the computer and see
  • Close Microsoft Outlook and related programs
  • Use Inbox Repair Tool
  • Recreate the OST file on your computer
  • Disable Cached Exchange Mode

Restart the computer and see

Restart the computer and see and see if Outlook launches properly.

This error indicates that the Outlook OST file is in use, which means there are probably some programs running in the background with the OST file. You should try to close MS Outlook and related programs in the Task Manager to fix the error.

  • Right-click the Start Menu and select Task Manager.
  • Under the Processes tab, right-click these programs one by one: Microsoft Outlook, Teams/Lync, UCmapi, Communicator, and Skype.
  • Then hit the End task option for each of them.

Use Inbox Repair Tool

Use the Inbox Repair Tool to recover items from damaged or corrupted. Ost file, or see if it can help with your Outlook data file issue. The OST Integrity Check Tool can also help you fix any corruption. Ost files you have.

Recreate the OST file on your computer

For all we know, the Outlook OST file has probably gotten corrupted, which is why you receive The file username. ost is in use and cannot be accessed in error. However, if you delete this OST file, Outlook will replace the file and fix the issue. Data won’t be lost by deleting or renaming this file, as the file will be recreated.

To rename the OST file on your computer, restart your PC and go to this location:

C:\Users\ACK\AppData\Local\Microsoft\Outlook

In the Outlook folder, navigate to the.OST file that is giving problems. You will see the name as, say, emailid@abc.com. Rename it to emailid@abc.com.bak.

Disable Cached Exchange Mode

If the solutions above didn’t work, disabling Exchange Mode on your computer is another method that has helped some Outlook users fix this error. You can follow the steps below to disable cached exchange mode:

  • Open the Control Panel on your computer and set the View by menu to small icons.
  • Click on Mail (Microsoft Outlook)
  • On the resulting pop-up, select Email Accounts.
  • Tap on your Outlook address and hit the Change
  • Uncheck the Use Cached Exchange Mode
  • Then select Next and click Finish.

The file username. ost is in use and cannot be accessed error should no more show whenever you open Outlook on your computer.

What is using the OST file?

An OST file is an Outlook data file that’s used when you have an Exchange account and want to work offline. The file stores a copy of your emails from the Exchange account on your computer. That way, you can access your emails even when you’re not connected to the internet.

Where is the Outlook OST file located?

The Outlook OST file is located in the: drive:\Users\user\App Data\Local\Microsoft\Outlook file. This stores your Outlook emails in the OST file for them to be available in offline mode. The file is automatically synchronized with the Outlook server.

What happens if I delete the OST file?

The OST file on your computer is not an issue since it can be downloaded again from the Exchange server. So if you need to, you can delete the OST file.

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