just follow these steps..
On the Tools menu, click E-mail Accounts.
Click Add a new e-mail account, and then click Next.
Click the Add button.
Click POP3, and then click Next.
Enter your e-mail account information.
In the Your Name box, type your name as you would like it to appear.
In the E-mail Address box, type your Yahoo! e-mail address, for example,
user@yahoo.com.
In the Incoming mail server (POP3) box, type pop.mail.yahoo.com.
In the Outgoing mail server (SMTP) box, type smtp.mail.yahoo.com.
In the User Name box, verify that everything before the at symbol (@) symbol of your Yahoo! e-mail address is displayed.
Enter your Yahoo! password.
Close everything and foloow these step to complete the set up..
1.From the Tools menu, click Accounts.
2.Click the Mail tab.
3.Click your Yahoo! Mail account, and then click Properties.
4.Click Servers.
5.Click to select the My Server Requires Authentication check box, and then click OK