Verify or update settings for AT&T email -
1. Right click your AT&T email and select Properties.
2. On the General tab: Verify your Name and Email address. ...
3. Select the Servers tab: ...
4. Select Outgoing Mail Server Settings and confirm the following: ...
5. Select the Advanced tab and confirm the following: ...
6. Select Apply and then OK.
Moreover, you can check out the website for SBCGlobal Mail login setup and configuration-related issues and their solutions - https://www.theemailhelpline.com/sbcglobal-net-email-login/