When saving a contact/lead/company and a duplicate is found, a pop-up is opened to warn the user. At the moment it is possible to skip this pop-up and duplicates are generally accepted then. So it should be possible to expand the settings, so that it can be customizable to avoid that users can skip the warning and are obligated to merge the contact or use another e-mail address instead. It would be nice to set this feature directly in the duplicate detection rule so that it can be decided per rule if it should be obligated or skippable.