Email Invitations

Most email clients will render a .ics file with mimetype text/calendar as a calendar invitation, and provide a link to add it to your calendar.

NOTE email systems are picky, for example, simply sending a invite.ics to google does not render RSVP buttons. See https://github.com/PHPMailer/PHPMailer/issues/175

Cancellations/Adjustments

As long as you provide a UID within your message, you may send followup emails that adjust the event. They will still need to be accepted.