Right now there is no way to stop the email notification at global level. The email notification whether to send or not completely depends on the notification preference of the recipient.
In order not to receive email notification for a particular user, you have to set the notification preference value to QUERY
the use of #WF_SECURITY_POLICY set to N_MAIL does work though it requires customization of the notification message in workflow builder. Still, as pointed by Saroja, this is a not a global or configuration approach; only prevents customized notifications from being sent.
A feature allowing such usability is being worked on and could be available by summer this year.