If you want a professional method to convert Yahoo Mail to CSV files, then you can try the SysInfo Yahoo Backup Tool. It backup Yahoo emails into PST, MBOX, CSV, EML, PDF, and other formats. It also imports Yahoo mailboxes to G Suite, Office 365, Gmail, and IMAP accounts. This tool supports migrating emails from a single as well as multiple Yahoo accounts. Moreover, it includes several features like a mail filter, removal of duplicate emails, and maintaining proper folder hierarchy. It is compatible with all versions of Windows OS.
Also Read: Export Yahoo to CSV File