This is on a site that I just updated from J! 3.10 to 4.2.8, PHP 8.0.27. Changing PHP back to 7.4 fixes the problem.
New users are not able to register, and the forgot login and profile edit functions are not working. In each case, entering valid information and submitting the forms results in the error message "The email domain is not allowed." Is that a CB message or a Joomla message?
Email server settings are correct. There is no email validation set in CB email field parameters. CB Anti-spam plugin is not installed.
Where to look for solution for PHP 8?