I do not have Cingular service but another GSM provider, who gave me a solution to the problem. I am assuming you have a similar Blackberry interface one you are logged in at Cingular.
1. Go into your "customize blackberry settings" sections accessible from your account on the Cingular website (sorry -not sure how that access looks)
2. Click on email options
3. Find where you can customize your blackberry settings
4. Click on "Profile"
5. Select "Customize your settings to receive messages from other email accounts."
6. Delete your existing account
7. Select "Add account"
8. Enter the following:
User name: a
Password 2: a
This will send you to more customized pages with more email options
9. Select "Internet Service Provider Email"
10. Add your email server and confirm port
11. Put in all the new info - correct this time
12. Select finish.
This took care of it for me, but if my vague instructions do not match your interface, I would call Cingular and they should be able to take care of it. Good luck. This was frustrating!