For Yahoo e-mails:

1. Click Tools-> Account Settings
2. Click Add-> Mail Account button.
3. Choose your display name. Click Next
4. Type your email address in the box. Click Next
5. Type 127.0.0.1 as the outgoing mail and incoming mail server. Port default is 25.
6. Type in account name and password.
7. Continue modifying any of your preferences in the account and then click on OK. 



Also, you should view the help file, it contains more information.....