When Microsoft Entourage is handling meeting updates or cancellations between Exchange users, it’s critically important that it can match up the change to an event with the correct event in a calendar. It does so by comparing unique identifiers between the update/cancellation message and existing calendar events. As nearly as I can tell, this depends on having the right UID, which makes sense.
How can you see the UID for events? Drag the event from an Entourage calendar to a Finder window, where it will become an vCalendar/iCalendar-formatted file with a .ics extension. You can open the resulting file in a text editor. Here’s a sample from a repeating event in an Entourage calendar, with the UID highlighted:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Microsoft Corporation//Entourage Mac 11.0 MIMEDIR//EN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:GMT -0500 (Standard) / GMT -0400 (Daylight)
X-ENTOURAGE-CFTIMEZONE:
BEGIN:STANDARD
TZNAME:Standard Time
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=11;BYDAY=1SU
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
DTSTART:16010101T020000
END:STANDARD
BEGIN:DAYLIGHT
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=3;BYDAY=2SU
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
DTSTART:16010101T020000
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
UID:040000008200E00074C5B7101A82E00800000000D0172C9CE47DC801000000000000000010000000C131C7E01B61184999585795596672E0
X-ENTOURAGE_UUID:37656211-A6ED-4E37-99D2-BAD25704AF63
DTSTAMP:20080304T160415Z
DTSTART;TZID="GMT -0500 (Standard) / GMT -0400 (Daylight)":20080305T100000
DTEND;TZID="GMT -0500 (Standard) / GMT -0400 (Daylight)":20080305T113000
LAST-MODIFIED:20080304T160433Z
… [snip]
Similarly, you can drag and drop a proposed change to an event, which is received by e-mail (because Exchange is largely an e-mail based — rather than a network-based — calendar system), to the Finder. This will save the message as the text source of the e-mail, with a .eml extension. That file can also be opened in a text editor, where you can see that it contains a siginficant amount of vCalendar/iCalendar data. Here’s a sample cancellation notice that removes one instance of the recurring event from Entourage — for reference, not the instance shown above, but another one from the same sequence:
BEGIN:VCALENDAR
METHOD:CANCEL
PRODID:Microsoft CDO for Microsoft Exchange
VERSION:2.0
BEGIN:VTIMEZONE
TZID:GMT -0500 (Standard) / GMT -0400 (Daylight)
BEGIN:STANDARD
DTSTART:16010101T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=11;BYDAY=1SU
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
X-MICROSOFT-CDO-MODPROPS;X-MODPARAM=1:attendee,BEGIN,class,created,description,dtend,dtstamp,dtstart,duration,END,last-modified,location,organizer,priority,recurrence-id,sequence,status,summary,transp,uid,x-microsoft-cdo-alldayevent,x-microsoft-cdo-apptsequence,x-microsoft-cdo-attendee-critical-change,x-microsoft-cdo-busystatus,x-microsoft-cdo-importance,x-microsoft-cdo-insttype,x-microsoft-cdo-intendedstatus,x-microsoft-cdo-owner-critical-change,x-microsoft-cdo-ownerapptid
DTSTAMP:20080422T194244Z
DTSTART;TZID="GMT -0500 (Standard) / GMT -0400 (Daylight)":20080423T100000
UID:040000008200E00074C5B7101A82E00800000000D0172C9CE47DC801000000000000000010000000C131C7E01B61184999585795596672E0
… [snip]
Note that the UID properties match.
If you are troubleshooting a problem where an update/cancellation does not modify an existing event as you expected, and the UIDs of each do not match, that’s probably the source of your problem. Of course, you still have to figure out why the UIDs don’t match. In that case, I’d personally start by looking at what other synchronization software (besides Entourage’s own Exchange sync) and devices are involved.