There are a number of different settings for connecting to Yahoo mail servers.

1. AT&T customers use the Yahoo server, smtp.att.yahoo.com and the SMTP Port 465 w/SSL checked
2. Yahoo Plus customers use the Yahoo server, plus.smtp.mail.yahoo.com and the SMTP Port 465 w/SSL checked.
3. Regular Yahoo customers use the Yahoo server, smtp.mail.yahoo.com and the SMTP Port 25 **

All Yahoo SMTP configurations require that you include User Authentication (your AT&T or Yahoo email address and password)

** If your Internet Service Provider (ISP) blocks Port 25, then you will have to use an alternate SMTP Port number such as 587. You can contact Yahoo to ask about alternate Port numbers to use in this case.