I recommend this eSoftTools OST to PST Converter software. You can fix the error that Outlook OST files are not in use and cannot be accessed. So it is 100% secure and risk-free for your device. All you users, both technical and non-technical, can operate the user software smoothly. It supports all types of Windows OS including Windows 11 versions. Give the free demo version a try and save 25 items from different folders of the OST mailbox.