Resolve Outlook OST file is already in use Error in Outlook

OST file i.e. also known as Offline Storage file/table is being created when Outlook is configured to work with IMAP or Exchange account. This OST file enables us to work in cached/offline mode. When we work offline this OST file is being used & gets updated and later being synchronized with Exchange Server to update itself and the online mailbox. Sometimes this OST file becomes inaccessible due to some issues or corruption in such a case you become unable to access the OST file components.

Ok, let’s consider a practical situation, suppose you are using Outlook and suddenly a message pops up as below:

“The file OST_File_Path\outlook.ost is already in use by the maximum number of applications. Close some of the applications, and then try again.”

This is one of the most common error message that Outlook users face regularly.

Why this error?
You get this error because either you are trying to access some corrupt OST file. Or your OST file is being used by so many applications and due to which it becomes irresponsive and Outlook is not able to communicate with it.

How to Resolve it?
If the error is due to the use of OST file by various applications, then proper restarting of the system will resolve the issue.

If the reason behind the error is not resolved after restarting the system, then the corrupt OST file is the reason behind this error. To recover OST file you have two options.

  1. You can recreate OST file. To recreate OST file backup OST file by renaming OST file. A new OST file will be automatically created with all current online mailbox content, when you get connected with the Exchange Server.
  2. Using this option you can recover the current online mailbox component, but what in case you have some important work done in the OST file and that is not synchronized with the Exchange Server. In that case you need to recover the OST file. Outlook comes with built-in utility named scanost.exe and scanpst.exe that can be used to repair/recover the OST file. Search your system to find both files and then use them to recover/repair corrupt OST file.
The built-in tool is not a reliable way to recover/repair the OST file, because the tool only woks in ordinary cases of OST file corruption. In serious corruption these utilities may fail and may also leads to further damage to the OST file.  So it always recommended backup the OST file before using the built-in tool to repair it. If the built-in utility fails to recover the OST file you can try third party tool to recover OST file components. Third party OST recovery tools are commonly known as convert OST to PST tool. Such convert   OST to PST tools are easy to use and converts the corrupt OST file into PST file which can be imported into Outlook.