I am working on custom SharePoint calendar which uses .NET code to render VCALENDAR payload with the email which I send to all attendees.
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.
Here is sample of my VCALENDAR which I am sending to all attendees to update existing recurring event:
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