iCalendar to force the 'Accept/Decline' buttons to appear in an updated event instance for Outlook?

Question

Does anyone know what iCalendar conditions I need to force the 'Accept/Decline' buttons to appear in an updated meeting message for Outlook 2007? Is there a combination of regular iCalendar fields, or some X-MICROSOFT fields I'm missing out on to force a re-accept? Our updates come far enough after the initial message to make a re-accept mandatory.

I see this note for Outlook 2007, and I'm hoping that some combination of values will force an 'Accept/Decline' - short of a change of value in DTSTART.

"If changes are made to meeting details, attendees receive an update with the changes highlighted, rather than having to reaccept the meeting."

--http://office.microsoft.com/en-us/outlook/HA100743061033.aspx

This problem occurs for updates to single, non-recurring, UID only meetings as well updates to recurring meetings using RECURRENCE-ID and UID.

We use the ATTENDEE line in the update such as:

ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;
   CN="Full Name":MAILTO:[email protected]

to attempt to force the Accept/Decline behavior.

Thank you everyone!

ICAL messages are below.

I needed to place the ATTENDEE records in the initial message to please Notes, but tested without those lines to the same effect. I also tried sending the initlal message as METHOD:PUBLISH and the updates as METHOD:REQUEST. The records update, but no new Accept button is offered in Outlook 2007. We bump the SEQUENCE number for each update.

INITIAL MESSAGE

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//Product/Platform/Name//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:America/New_York
X-LIC-LOCATION:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:[email protected]
RRULE:FREQ=WEEKLY;INTERVAL=1;UNTIL=20091129T000000Z;BYDAY=SA
DTSTART;TZID=America/New_York:20091114T180000
DTEND;TZID=America/New_York:20091114T190000
SUMMARY:Sub Test 7
ORGANIZER;CN="'Meeting'":MAILTO:[email protected]
DTSTAMP:20091027T212241Z
STATUS:TENTATIVE
SEQUENCE:5
CLASS:PUBLIC
TRANSP:OPAQUE
ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN="Full 
 Name":MAILTO:[email protected]
ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN="Full 
 Name":MAILTO:[email protected]
END:VEVENT
END:VCALENDAR

UPDATE MESSAGE

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//Product/Platform/Name//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:America/New_York
X-LIC-LOCATION:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:[email protected]
RECURRENCE-ID:20091114T230000Z
DTSTART:20091114T230000Z
DTEND:20091115T000000Z
PRIORITY:5
SUMMARY;LANGUAGE=en-US:Sub Test 7
LOCATION;LANGUAGE=en-US:Access Code XXXXXXX
DESCRIPTION;LANGUAGE=en-US:Sub Test 7
ORGANIZER;CN="'Meeting'":MAILTO:[email protected]
DTSTAMP:20091027T222122Z
LAST-MODIFIED:20091027T221822Z
STATUS:CONFIRMED
SEQUENCE:7
URL:http://ical.server.org/calendar/detail.shtml?event
 _id=5088&instance_id=5385&recurrence_id=20091114T230000Z
ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN="Full 
 Name":MAILTO:[email protected]
ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN="Full 
 Name":MAILTO:[email protected]
CLASS:PUBLIC
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

Answer 1

To force Outlook to show Accept/Decline buttons again you must change one of the following:

• DTSTART
• DTEND
• Recurrence

See this very thorough article for more details.