The Yahoo7 official help doesn't set up the new y7mail POP access correctly. If your Yahoo ID is example@y7mail.com, according to the help document, you should configure it as follows:
Server Settings
Incoming Mail Server (POP3):
pop.y7mail.com
Use SSL, port: 995
Outgoing Mail Server (SMTP):
smtp.y7mail.com
Use SSL, port: 465, use authentication
Account Name/Username:
example
Email address:
example@y7mail.com
Password:
Your Yahoo!7 Mail password
However, following this guide, unfortunately, you cannot access the y7mail through software like outlook or thunderbird, because there will be a password error message. To overcome this, change the account name or username to example@y7mail.com, ie, the Yahoo ID. The error won't appear again.