Guides
Longer answers to the questions publishers actually search for. Browser facts are dated and sourced, and every guide says what it does not know.
Notification fatigue: how to measure it and how to reduce it
Notification fatigue is a subscriber who has stopped reading your notifications and has not told you yet. You reduce it by capping exposure per person instead of per campaign, and by enforcing that cap before the send rather than reading about it in a dashboard afterwards.
Push notification frequency: how often should a news site send?
There is no correct number, and any source that gives you one without naming its sample is selling something. What exists is a ceiling the browser enforces, a budget your readers set, and a floor set by what a send is worth. This is how to find your own number.