If you are still unable to open your OST file in Outlook, then you need to first convert OST to PSt and then import it into Outlook. To complete the import process you will need an automated tool. One such approach is the Advik OST to PST Converter tool. The software allows you to open orphan or inaccessible OSt file into Outlook 2021, 2019, 2016 and all other editions effortlessly.
Steps to open OST file into Outlook interface -
1. Run the software on your system.
2. Add the OST file to the software.
3. Select the email folder you want to convert.
4. Choose PST from the saving options.
5. Browse the targeted location and hit the Convert button.
6. Open Outlook and using Import/Export tool import the exported data file into Outlook.
Done! Here complete the process, now you can easily open OST file into the Outlook mailbox.