Mailman sends you an email notification about new emails that ended up in the moderation queue, and a periodic (and fairly frequent) reminder about the queue being non-empty. The latter is IMO a waste of time: I want to be able to ignore emails which I don't want to allow through. I'll batch discard them once every blue moon but I don't want to spend time dealing with them individually. Also I want to rely on my mail client's spam filter to not even show me notifications about obvious spam most of the time. These reminders break that. (Sure, I can just set up a filter for them, so this bug is not a high priority. But a central fix would be nicer.)
I can't recall the exact setting but it was possible in Mailman 2 to disable the reminders and only get one notification about each new held up email to the list. I can't find a way to do the same in Mailman 3.