Several Outlook users are getting the message “Ost username file is in use and cannot be accessed” when they try to use the program on their PC. The error simply indicates that an Outlook data file named username.ost is in use and the program is not running on your computer due to this. Additionally, this Outlook error occurs for users who have enabled the “Use Cached Exchange Mode” option in their Outlook account settings and therefore their emails are downloaded and stored locally in a file named username.ost. Hence, they can access their Outlook emails offline and the emails will be synced back to the exchange server once they are back online.
Outlook Data File – C:UsersAppDataLocalMicrosoftusername .ost file is in use and not accessible. Close all applications using this file and try again. You may need to restart your computer.
However, when your computer or Outlook crashes while syncing with the Exchange server, you may start getting the username.ost file used and unavailable every time you try to start Outlook, which blocks the program from opening. The error occurs because the username.ost file is still in use on your PC or is corrupted due to a crash. After discussing this Outlook error, we’ll look at proven methods to resolve the issue and get the app back up and running.
Causes of Outlook error with ost file username not accessible.
The known reasons why the username.ost file is used and cannot be accessed in Outlook are as follows:
- Corrupt OST file.
- Lack of synchronization between the OST file and the Exchange server.
- Conflicting usage of OST file.
Fix Username of ost file is in use and not available for Outlook error.
Whenever you receive the error message “The file username.ost is in use and not available” when you try to start Outlook on your computer, you must first restart your computer. If the problem persists, try to resolve it with the solutions below.
- Restart your computer and see
- Close Microsoft Outlook and related programs
- Use the Inbox Repair Tool
- Recreate the OST file on your computer
- Disable Cached Exchange Mode
1]Restart your computer and see
Restart your computer and check if Outlook starts correctly.
2]Close Microsoft Outlook and related programs.
This error indicates that an Outlook OST file is in use, which means that some programs may be running in the background with the OST file. Hence, you should try to close MS Outlook and related programs in Task Manager to fix the error. Here’s how to do it:
- Right click start and select task manager .
- Under Processesright click these programs one each: Microsoft Outlook, Teams/Lync, UCmapi, Communicator, and Skype.
- Then click End task for each of them.
Once done, restart Outlook and see.
3]Use Inbox Repair Tool
Restore your Outlook OST personal data files and see if that helps. The Inbox Repair Tool can recover items from an offline folder or .ost files. The OST Integrity Check Tool will help you fix corrupted .ost files.
4]Recreate the OST file on your computer.
As far as we know, the Outlook OST file has probably been corrupted, which could be the reason you are getting the error message. The username.ost file is in use and not available. However, if you delete this OST file, Outlook will be forced to replace the file and thus fix the problem for you. You don’t have to worry about losing any data when deleting or renaming this file, as the file will be re-created.
To rename the OST file on your computer, restart your computer and navigate to this location:
C:UsersACKAppDataLocalMicrosoft Outlook >
In the Outlook folder, navigate to the .OST that is causing problems. You will see the name as, say, [email protected]. Rename it to [email protected].
Now open outlook, and hopefully the issue will be resolved.
3]Disable cached exchange mode
If the solutions above didn’t work, disabling Cached 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 on control panel your computer and install View by to small icons.
- Press Mail (Microsoft Outlook).
- In the pop-up window that appears, select Email Accounts.
- Click on outlook address and hit change.
- Clear the Use Cached Exchange Mode check box.
- Then select Next and press Finish.
With one of the methods above, the username.ost file is in use and cannot be accessed, the error should no longer be displayed whenever you open Outlook on your computer.
What does the OST file use?
An .ost file is an Outlook data file that is used when you use the default Outlook Cached Exchange mode or have selected an Exchange account and want to work offline. The file basically stores copies of emails from Exchange or Outlook .com accounts on your computer so that you can access them without an internet connection.
Where is the Outlook OST file located?
The Outlook OST file is located on the drive: UsersuserAppDataLocalMicrosoft Outlook > . This file stores Outlook emails in this OST file in the above location on your computer so that they are available offline. This file is automatically synchronized with the Outlook server to get them on the same page.
What happens if I delete the OST file?
There are no problems with the OST file on your computer as it will be downloaded again from the Exchange server. Therefore, if you need it, you can delete the OST file.
In this article, we explained that the file with the username ost is in use and cannot be accessed due to an Outlook error. Feel free to let us know if you have questions or comments about this article. Leave a comment below and useguide.net will reply as soon as possible.