This article was previously published under Q244330
When you start Outlook, you may receive the following error message:
File <drive and path>\xxxx.pst is in use by another application. Close Microsoft Exchange and all other mail-enabled applications and try again.
Cannot open your default e-mail folders. The file <drive and path> outlook.pst is in use and cannot be accessed. Close any application that is using the file, and then try again. You might need to restart your computer.
This problem occurs even if you have full access permissions and there is no password on the Outlook Data (.pst) file. The problem may appear intermittently. This can also affect an Offline Outlook Data (.ost) file.
This problem can occur if the .pst or .ost file is being accessed by a backup program. Larger .pst or .ost files take longer to back up and are more prone to this issue if the backup is running while someone is trying to access it.
To resolve this problem, stop the backup job, or wait for the backup to finish and then start Outlook. Additionally, you should contact the third-party vendor to confirm that you have the latest updates installed and to report the problem.
You can use one of the following workarounds to try to prevent the error.
Schedule the backup program to run at a time that you are not using Outlook
Exclude the Outlook data file name extensions from the backup: *.ost and *.pst