To convert OST to PST without using Outlook, you need an
OST to PST converter software such as CubexSoft OST Converter. By using this software, you can convert large, orphaned, and inaccessible OST files to PST. After conversion, you can open the PST file in any Outlook account and access the mail items. This software also supports multiple file formats such as PDF, MBOX, EML, MSG, DOC, RTF, TXT, Office 365, Gmail, G Suite, and many more. It was compatible with all the versions of MS Windows OS and Mac OS.