If you want an easy way to import PST to Yahoo Mail, you can try the BitData Migration Outlook Converter. The tool lets you add PST files using Select Files or Select Folder options and supports more than 20 export formats, including Exchange Server, Windows Live Mail, Yahoo, Thunderbird, PNG, BMP, Office 365, EML, MSG, HTML, MBOX, DOC, MHT, CSV, and others. Its interface is simple enough for beginners yet offers advanced features for users who want more control over the conversion. You can also use the free demo version to test how it works and convert the first 25 PST items at no cost.