OST file for offline backup. You can manually export all Outlook data from an old OST backup file in your computer to your Office 365 account by exporting OST file data to PST file using Import/Export wizard in Outlook and then upload the PST file to Office 365 using network upload method.
This manual method is very complicated and lengthy. There is also a risk of data loss during this process. vMail OST Converter is an email conversion tool which can scan all data from the ost file and directly export to Office 365 in just a few steps without losing any data. User-interface of this tool is very simple and easy-to-use. This OST file converter supports OST files from MS Outlook versions 2019, 2016, 2013, 2010 and older.
Learn More- Export OST to Office 365