I would like to suggest you can also try Mailsbackup Yahoo Backup Tool to backup Yahoo Emails to hard drive, PC or webmail. It easily download Yahoo Mail emails with 30+ saving options to take backup of Yahoo email account. Users can migrate Yahoo emails to Outlook, Gmail,- Outlook.com, Office 365, Exchange Server, etc.This tool enables user to backup multiple Yahoo Mail accounts without any limitations.

Check for more details at:  https://www.mailsbackup.com/yahoo/