The Bellsouth email not working on iPhone due to the following reasons.

• Step 1:Incorrect server settings
• Step 2: Wrong configuration method
• Step 3:Incorrect user name and password

To resolve this problem on your iPhone, you have to remove the BellSouth email account and re-configure it.Before proceeding with the re-configuration steps, remove the BellSouth email account from the iPhone.

• Step 1: After pressing the Home button on the iPhone, tap the Settings application icon followed by the Mail, Contacts, Calendars option.
• Step 2: Touch Add Account  Other  Add Mail Account if the Bellsouth email not working on iPhone.
• Step 3: Provide the BellSouth email accounts information in the Name, Email, Password, and Description fields and tap the Next option.
• Step 4: On the New Account screen, tap the IMAP or POP tab.
• Step 5: Also, complete the incoming and outgoing server settings with the correct information.

Incoming Mail Server

• Server Host Name for POP - pop.mail.att.net
• Server Host Name for IMAP - imap.mail.att.net

Any one of these hostnames should be entered in the Incoming Mail Server’s Host Name field.Outgoing Mail Server

• Step 1: Server Host Name (SMTP) - smtp.mail.att.net
• Step 2: After entering the BellSouth email account’s email address and password in the appropriate fields, touch the Next button followed by the Save button.
• Step 3: To change any server settings, go back to the Accounts & Passwords screen and tap the email address of the BellSouth email account.
• Step 4: Tap the Advanced option and check if you have turned on the toggle next to the Use SSL option.
• Step 5: Make sure the Server Port field is 993 (IMAP) or 995 (POP) then to check the Bellsouth email not working on iPhone or not.

Source: https://mailsetup.online/fixed-bellsouth-email-not-working-on-iphone