To move OST files into an Office 365 account, first, convert the OST file to PST using a third-party tool. Then, use the Office 365 Import Service or Outlook to import the PST file. Direct OST Import Not Supported by OST files to Office 365.
Convert OST files to Office 365 using migration tools or methods. Before importing data to Office 365, OST files must be converted to office 365 account PST (Personal Storage Table). This conversion can be done using Outlook's "Import/Export" feature or third-party tools.
