A 1) Please choose "Add Account" on "Settings" page.
2) Please choose "Others" instead of "Yahoo!Mail" on "Select Service" page.
3) Please set up in taking these steps below ;

【Incoming mail server】

Host : plus.pop.mail.yahoo.com
User : your full email address
SSL : ON
Authentication : Password
Server Port : 995

【Outgoing mail server】

Host : plus.smtp.mail.yahoo.com
User : your full email address
SSL : ON
Authentication : Password
Server Port : 465