No OOB global configuration.Only manual way.
In individual user login- Account settings - Notifications-Project (Email) needs to be unchecked.If there are more users you can send an communication to users.Asking them to un-check this.
But if you think it should be done with out user interference and if it is important then you can try the below UN-supported way.Get CA approval and an proper testing.
Oracle DB:-
-- To check the Email tab for projects under account settings - notifications
delete from CLB_NOTIFICATION_PREFS where USER_ID = 5002002 and notification_type='NOTIFICATION_PROJ_PARTICIPANTS' and method = 'EMAIL';
-- To uncheck the Email tab for projects under account settings - notifications
INSERT INTO CLB_NOTIFICATION_PREFS
SELECT SYSDATE,1,SYSDATE,1,ID,'NOTIFICATION_PROJ_PARTICIPANTS','EMAIL' FROM CMN_SEC_USERS
WHERE ID =5002002 ;
COMMIT;
You can put this inside an procedure and schedule as an Job.
Even you can try for an DB trigger which is up to you.
cheers,
sundar