Calendar Event Invites with 3 Button Reply
In this example, the Calendar service is provided by Apple
Many corporations have their own internal Calendar service.
Microsoft and Gmail and other ISP's also provide their own Calendar service.
The Calendar service (Apple) created and sent the email
The email is sent from email@example.com
So if it's going to work with our mailing list, then firstname.lastname@example.org needs to be added to the Post Only list.
The body of the email contains the 3 specially crafted buttons
The traditional ICS attachment is also included
If buttons are clicked, they contact the Calendar service (Apple)
Or the ICS attachment can be clicked on to see the event particulars.