I have a bellsouth.net address and have had no problems. I let the system configure and I've had no problems receiving or sending email. Also, I don't have any of the email patches on my phone. All of the ATT.net mail is (or should be) handled through yahoo. As the changeover is being made you can expect tremendous difficulty if you are still pointing to the old att.net servers (went through hell on our laptops but haven't had problems on the phones). You might try deleting the account on your pre and then setting it up again.
The phone set me up with an IMAP service.
Incoming mail server= palm.imap.mail.yahoo.com
username= your fully qualified email address (ie
yourname@bellsouth.net)
port# 993
encrytion=SSL
Outgoing mail server = palm.smtp.mail.yahoo.com
Use authentication=ON
username= fully qualified email address as above
port# 465
Encryption=SSL
Hope this helps.