A store administrator can enable and disable email notifications directly on the notifications listing page in the store Admin area (Store setup -> Email notifications).
Email notifications are sent separately for every user type enabled in a store. Hence, they can be enabled and disabled on a per-user-type basis.
To enable/disable a notification for a user type, it is necessary to set the corresponding toggle either ON or OFF.
In case the ON/OFF toggle is in faded-green, a notification can not be disabled for this type of user.