Hi All, I think it is better to be able to activate email notifications directly on the Calendar Event rather than in Email Digest:
The Upcoming Calendar Events in Email Digest sends notification for all open calendar events including events created by other users.
But if the user can activate the notification as he creates the Calendar Event, that will enable him restrict notification to that event only.
The user should be able to choose more than one recipient as he creates the Calendar Event.
Thank you.
NB: Also opened a request for on GitHub:
https://github.com/frappe/erpnext/issues/15344#issue-357995395