As admin go to Site administration -> Plugins -> Authentication -> Manage authentication Add 'example.com .moodle.com' to 'Allowed email domains' list and Save Changes Logout as admin Create a new user account with email = 'something@EXAMPLE.COM' and Save changes. Check new user has been created. Create a new user account with email = 'something@example.MOODLE.COM' and Save changes. Check new user has been created. Create a new user account with email = 'something@something.com' and Save changes. Check new user has not been created. As admin, go to Site administration -> Plugins -> Authentication -> Manage authentication Remove 'Allowed email domains' list Add 'example.com .moodle.com' to 'Denied email domains' list and Save Changes Logout as admin Create a new user account with email = 'something2@EXAMPLE.COM' and Save changes. Check new user has not been created. Create a new user account with email = 'something2@example.MOODLE.COM' and Save changes. Check new user has not been created.  Create a new user account with email = 'something2@something.com' and Save changes. Check new user has been created.