First of all the user needs to make sure to have a good internet connection as bad internet connectivity leads to this issue.
Then check whether the server is enabled or not.
Change the IMAP settings to the POP server settings as changing the server setting will solve this issue.
Simply remove the SbcGlobal email from the device and again follow the steps to install it.
Also, the user should switch off their iPhone and should then make it work accordingly. After a few minutes, the user should switch on their phones and should see whether the issue is solved or not.
Then select and press the hold and the sleep button with the volume keys simultaneously for making it work in the better way.

SBCglobal email login | SBCglobal email settings | SBCglobal mail settings