The main reason why you are unable to connect to the server is because the email settings you used are incorrect. You can have a look at the SBCGlobal sever settings given below to verify and change the settings accordingly:
Email protocol POP3
• Inbound server inbound.att.net
• Inbound port 995
• SSL: Yes
• Outbound server: outbound.att.net
• Outbound port: 465
Email protocol: IMAP
• Inbound server: imap.mail.att.net
• Inbound port: 993
• SSL: Yes
• Outbound server: smtp.mail.att.net
• Outbound port: 465 or 587
In case you still cannot connect to the server you can call the sbcglobal technical support number and ask for help. Email experts and software technicians are available 24 hours a day to give you the best solutions for any error related to your SBCGlobal account.

For more info click here: sbcglobal customer care | sbcglobal phone number