In Outlook.com Calendar, I subscribe to a few public calendars as well as share multiple calendars with my family. For one of those calendars, I had enabled notifications when events are added or changed. In recent weeks, the calendar notifications are coming non-stop. There have been about 20 or so legitimate changes, but I am getting THOUSANDS of notifications. Both of my kids are having the exact same problem that I'm having, and both of them have actual outlook.com email addresses. The only person in the shared calendar group not experiencing this issue is my wife, who is the original creator of these shared calendars.
We are going to have to disable the notifications for now, but we hope you can fix this issue soon.