How to unsubscribe users from email notifications via API

Hi all,
I am looking for away to unsubscribe a user from all email notifications (as admin). I have my own Gitlab instance.

I can change projects’ or groups’ notification settings, but I couldn’t find a way to change them for a user - neither via API nor via the UI.

Specifically, I don’t want the user to get an email once that user is granted access to a project. Turning off all notifications for that project (that is, setting them to disabled) does not seem to be enough.

More info

I create users via the API with force_random_password and skip_confirmation. In other words, the user doesn’t necessarily now he’s registered to this gitlab instance.

Thank you very much in advance,