I am currently developing an Outlook Add-In that receives a notification whenever a change in the user's calendar is recorded. The thing is that, there are some occasions where we would change an event's date from the backend by calling PATCH /events/eventId.
It would be very nice if there was any way to notify the user immediately, other than sending an email. Something like a popup modal with a warning message would work very well.
Currently the feature you requested is not a part of the product. We track Outlook add-in feature requests on our user-voice page. Please add your request there. Feature requests on user-voice are considered, when we go through our planning process.