Here is the ATT response to not supporting Vista!
Thank you for contacting AT&T Internet Services E-mail Support.
I understand how frustrating it is that you are having problems sending
emails using your Windows Vista email client. I sincerely apologize this
email setup issue has caused you. I recognize the importance of getting this
fixed at the soonest possible time. I will be glad to provide you the
information and guide you to the right direction.
With regards to this issue, I have checked the policies and all our tools to
verify if we support this operating system or this email client, Windows
Vista. Unfortunately Red, we sincerely regret to inform you that this
Operating System or Email Client is not supported at this time.
As much as we want to support your email setup, we cannot make a fair
conclusion as how to configure or check your Windows Vista as we are not
trained with this kind of software. I hope that you understand our
limitations on this matter. I would recommend that you contact the
manufacturer of that software to provide you assistance with your email
client. Here is the number where you can contact Microsoft Technical
Support, 1- 800-936-5700 or at the link:
http://support.microsoft.com/