Redmine

I want a method to stop/run email notification every acount.

Because there are users who do not have an Email address.

case1
They are outside subcontractors. They do not login Redmine.
In management, a project leader assigns them to a ticket on Redmine only.
The email notification of Redmine to them is not necessary.
The project leader contacts them by other methods.

case2
In my office rule, there are really peaple who do not have an Email address.

I set a dummy Email address for them now.
It is not preferable to send a mail by an invalid address, so I set all email notification for invalidity now.