Note:
You can override a setting at a lower level (for example, configure Notification Type to Every 2 hours, and override one of the Conditions to Immediately). Then the parent setting(s) displays the word Mixed, to provide a visual indication that more than one preference setting has been assigned to child level settings. You can change the value from Mixed to a different preference setting; the child level settings are changed to the new setting.
If an Administrator disables the System Settings Configuration Settings for Email Notifications, then notifications are suspended. See Enabling Email Notifications.