title: Is there a standard and an implementation for Icalendar event RSVP
body: <p>The summary is that I am now implementing an event confirmation system and can't find the right format for the ICalendar replies. Therefore I wonder if there is an example out there of complete REPLY message and maybe a PHP library that would wrap it all?</p>
  <p>Now for the details, we get external emails including event invitations asking for RSVP. Here is an excerpt of the iCal file:</p>
  <p><code>ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN=&quot;'user@company.com'&quot;:MAILTO:user@company.com ORGANIZER;CN=&quot;Organ Izer&quot;:MAILTO:organizer@company.com</code></p>
  <p>I couldn't find the reply standard to send the RSVP to the organizer. The <a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.2.12" rel="nofollow noreferrer">RFC 2447</a> mentions &quot;ATTSTAT&quot; and &quot;PARTSTAT&quot; parameter.</p>
  <p>By trying to mail the following message to Google calendar the event is not being updated.</p>
  <pre><code>$headers = &quot;Content-Type:text/calendar; Content-Disposition: inline; charset=utf-8;\r\n&quot;;
  $headers .= &quot;Content-Type: text/plain;charset=\&quot;utf-8\&quot;\r\n&quot;;
  $headers .= 'BEGIN:VCALENDAR
  VERSION:2.0
  METHOD:REPLY
  BEGIN:VEVENT
  ORGANIZER;CN=JCharles:mailto:abcdef@gmail.com
  UID:oc7ae7537999onscsivg8km123@google.com
  ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=CONFIRMED;RSVP=
   TRUE;CN=jc@company.se;X-NUM-GUESTS=0:mailto:jc@company.se
  LOCATION:
  SEQUENCE:1
  END:VEVENT
  END:VCALENDAR';
  
  mail('abcdef@gmail.com', 'Accepted:', &quot;Event accepted&quot;, $headers);
  </code></pre>
  <p>Is there anything wrong with the Ical message or with the method in itself? Is this the way the event replies are supposed to be sent?</p>