Calendar event invites with 3 button reply

Many corporations have their own internal Calendar service.

Apple, Microsoft, Gmail and other ISPs also provide their own Calendar service.

Example: Apple Calendar service

Apple creates and sends the email.

The email is sent from

If this invite is being sent to your Mailing List, then needs to be added to the Post Only list. Step-by-step instructions for adding to Post Only are included here.

The body of the email contains the 3 specially crafted buttons.

Often, the button options are Accept, Decline, and Maybe.

The traditional ICS attachment is also included.

Click the ICS attachment to see the event details.

What happens when someone clicks one of the invite buttons?

The Calendar service is contacted when a recipient clicks a button.