> Account: 'pop.att.yahoo.com', Server: 'smtp.att.yahoo.com', Protocol:
> SMTP,

maybe your pop/smtp servers should be respectively
pop.mail.yahoo.com (Use SSL, port: 995)
smtp.mail.yahoo.com (Use SSL, port: 465, use authentication)

http://help.yahoo.com/l/us/yahoo/mai...op/pop-30.html

Regards

--
Olivier C