New
#1
After being severely hacked, Yahoo is reacting by trying to shoehorn everyone into using 2-factor authentication and more robust protocols than POP3.
They don't really have their own application / off-line mail client; they just prefer that you log into their web site, so that you can view their ads as well as your mail.
W10 Mail is as secure as any other program running the same protocols (IMAP or POP3).