title: Updating Recurring vCalendar Event
body: <p>I am working on custom SharePoint calendar which uses .NET code to render VCALENDAR payload with the email which I send to all attendees.</p>
  
  <p>So far my implementation is working great except for updating recurring events. Outlook didn't able to recognize modified DTSTART/DTEND when I send updated VCALENDAR with same UID. Look like I am missing particular field for recurring events.</p>
  
  <p>Here is sample of my VCALENDAR which I am sending to all attendees to update existing recurring event:</p>
  
  <pre><code>BEGIN:VCALENDAR
  METHOD:REQUEST
  PRODID:Microsoft CDO for Microsoft Exchange
  VERSION:2.0
  BEGIN:VTIMEZONE
      TZID:tz
      X-MICROSOFT-CDO-TZID:10
      LAST-MODIFIED:20111229T172655Z
      BEGIN:STANDARD
          DTSTART:20111106T020000
          TZOFFSETTO:+0000
          TZOFFSETFROM:+0000
      END:STANDARD
      BEGIN:DAYLIGHT
          DTSTART:20120313T020000
          TZOFFSETTO:+0100
          TZOFFSETFROM:+0000
      END:DAYLIGHT
  END:VTIMEZONE
  BEGIN:VEVENT
      SUMMARY:Simple Event\, Attendees:Tin Tin 
      ORGANIZER:MAILTO:tin.tin@acme.com
      ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN=;X-NUM-GUESTS=0:mailto:tin.tin@acme.com
      ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN=;X-NUM-GUESTS=0:mailto:tin.tin@acme.com
      LOCATION:Conference Room
      DTSTAMP:20111229T172652Z
      UID:D26B0632-8496-4E76-977F-E7A04AF4CF4D
      SEQUENCE:1
      URL;VALUE=URI:http://acme/Lists/Conf/DispForm.aspx?ID=1178
      DTSTART;TZID=tz:20111229T140000
      DTEND;TZID=tz:20111229T150000
      RRULE:FREQ=WEEKLY;INTERVAL=1;BYDAY=TH;WKST=SU
      END:VEVENT
  END:VCALENDAR
  </code></pre>