I'd like to recommend the PassFixer OST to PST Converter software, which allows you to open OST files without Outlook and import them into Outlook. This software is quite popular and safe for all users. The utility can convert large numbers of OST files to different Outlook extensions and formats, including OST to Office 365, OST to MBOX, OST to Zimbra, OST to HTML, and others.
As a result, I strongly advise you to use this software.
More Info – Open OST file without Outlook
