To migrate OST emails to an Office 365 account, first convert the OST file to a PST format using tools like vartikasoftware Converter or vartikasoftware for OST to PST. Once converted, import the PST file into Office 365 via Outlook's Import/Export wizard or use Microsofts Office 365 Import service for larger migrations. https://www.vartikasoftware.com/product/vs-ost-to-office365-converter.html