You will need IMAP and POP3 setting as shown below to access your att net IMAP settings from a desktop email desktop program: Below are the POP3 incoming and IMAP outgoing mail servers and also the News server for AT&T ATT a preferred Internet Service Provider.
IMAP Settings
Hostname: imap.mail.att.net
Port: 993
Encryption: SSL
User name: Your full email address
POP3 Settings
Hostname: inbound.att.net
Port: 995
Encryption: SSL
User name: Your full email address