Native Notifications (on devices)
Any calendar entry should provide the possibility of being reminded. Instead of an email I would suggest to use the notification mechanism provided by the iOS/Android calendar apps. I think that most of the users will sync their calendar with a mobile device. An email is not the right medium for instant reminders in my eyes.
We already fully support this since fruux exists. Once you set up your Mac/iOS (or any other supported device: https://fruux.com/supported-devices/) the calendar (and todo-list on devices that have a todo-list app) will just use to local notification system of the device.