You can easily import OST files into Yahoo Mail using the SysInfo OST to PST Converter Tool. This helps you move all your emails, contacts, calendars, and tasks from an OST file directly to your Yahoo Mail account. It keeps your folder structure the same and doesn’t lose any data. Even if Outlook isn’t installed, you can still access your OST files in Yahoo Mail with this tool.
Read more: https://www.sysinfotools.com/ost-to-pst-converter.php