If you have trouble logging in to your AT&T email account you should check if the Internet Message Access Protocol (IMAP) settings are correct. The following IMAP settings need to be configured on your iPhone when you log in:
• Incoming mail server: imap.mail.att.net
• Incoming server Port: 993
• SSL (Incoming Server Security): SSL
• Outgoing mail server: smtp.mail.att.net
• Outgoing server Port: 465
• Authentication Required: Yes
If the IMAP settings are correct but you still cannot log in to your account you can call the AT&T Technical Support Numberand ask for additional assistance to troubleshoot the problem.

Read more: ATT Technical Support

Visit here: ATT Customer Service Number