The manual methods mentioned above can help you fix problems related to MS Outlook. If it succeeds, you can remove the add-in permanently. Running MS Outlook in safe mode will disable the add-ins, and you might be able to open the OST files with it.
‘OST file cannot be opened’ is one of the most discussed errors related to Outlook. Apart from this, there are various errors that make it impossible for users to open their OST files.
However, while accessing an offline OST file, sometimes users may receive an error, which says ‘OST file cannot be opened.’ According to many queries submitted on Microsoft forums, this error is majorly reported in Outlook 2016.
OST files are created by Outlook in an Exchange server environment to allow Exchange users to access the mailbox data and work in offline mode.