In my setup, I do have a "robot user" who is used by the 'create or comment' e-mail handler.

As the reporter, this user always gets e-mails when anything happens to the tickets, which unnecessary fills my inbox.

I want this user to be able to say "I don't want to receive any e-mail notifications" to stop the reception of those e-mails.

Support staff also suggested using cusomt notification schemes, but since in this projects there are also humans who want that notifications, this doesn't work.

Another use case would be a user who really wants to be cut out of communication but keep his / her account "for future use (tm)".

I'd suggest putting this setting into the "profile" page, next to where I define whether I want to be notified about my own changes (see the 'beautiful' mockup i attached)