What happens if I attempt to send an invitation from the Calendar app to an email address that doesn't have an associated Apple ID?
I just tried with one of my friends' email. They receive the mail with buttons like accept, decline etc., and the info of the event of course. The said buttons have URL like: https://www.icloud.com/calendar/eventreply_full/en-gb/&lt;some Key&gt;&amp;cc=IN#reply=accept It was sent from noreply@email.apple.com but with my name in the Sender. 

.ics of the event, text and HTML files were also attached.