ATT error code 553 denotes the issue in sending and receiving emails, and that may occur when it fails to communicate the main server. Poor configuration of SMTP and POP3 server settings may be responsible for the issue. so you need to find out the probable reason for the issue first to get the solution. You have to change the internet settings, email settings, and also review the browser settings. You should also check the internet connection. If still, you are getting some issues then you should call at contact att email customer support phone number and get the complete support from the expert community.