An OST (Offline Storage Table) file is a data file created by Microsoft Outlook to store a copy of your mailbox data from an email server locally on your computer. It allows you to access and work with your mailbox data even when you are not connected to the internet or the email server. OST file is a replica of Exchange mailbox and cannot be accessed outside the same environment.
So, if you are facing OST file cannot be opened issue then you need to know that OST file is a server side encrypted file and it cannot be accessed without same profile. Also once the OST file get disconnected with exchange profile, then it becomes orphaned. Microsoft does not provide any solution to access orphaned OST file.
There are multiple reasons that can result in error while accessing OST file. But don't worry there is one solution for all causes that results on OST file cannot be accessed error.
Microsoft clearly mentions that, they do not support to access any corrupted, inaccessible, and orphaned OST file even in same Profile. But don't worry there are third party tool that allow users to export OST file and save into Outlook data file.
Lets task about the solution for OST file cannot be accessed issue. In this case simply export OST file into PST format and add the PST file into Outlook using inbuilt import/export utility.
Use SysTools OST to PST converter and change OST file extension into Outlook supported PST file format. The software has multiple feature and advanced options that you user can understand from official web page.
Product page link: https://www.systoolsgroup.com/converter/ost-pst.html
Informative Post Link: https://www.systoolsgroup.com/updates/import-ost-file-to-outlook-2016-2013-2010/