I would like to recommend you can also try eSoftTools OST Recovery software to bulk Transfer Outlook Emails to Yahoo Mail. This utility is fully supportable with all OST Outlook files 2003, 2007, 2010, 2013, 2016. Users can easily install this utility and Windows OS XP, 7, 8, 10. It also ensures users can save their entire emails in the same folder and subfolder of their results. It can enable it to perform the conversion task from the OST file. A free demo file is available to transfer Outlook emails to Yahoo Mail.