Consider the following scenario:
- User receives the message when removing the email address of an existing Customer from the user interface.
User receives the same message when updating Customer records through CSV Import to set the Email field to null.
This occurs if in the Customer record > System Information tab > Access subtab > Give Access checkbox is set to True (marked). This makes the Email field required since it is needed to log in to Customer Center. Set Give Access = False to be able to remove the email address in the Customer record.