The message text was something like this:
From: Microsoft Outlook On Behalf Of Susan Smith
Sent: Monday, November 30, 2015 7:00 PM
To: John Roberts
Subject: Canceled: Management Meeting
When: Occurs every 1week(s) on Tuesday effective 1/1/2015 from 9:00 AM to 11:00 AM (UTC-06:00) Central Time (US & Canada).
*~*~*~*~*~*~*~*~*~*This meeting has been canceled by the organizer.This meeting has been canceled by the organizer. To see the original contents of the meeting, view the item in your calendar._____Sent by Microsoft Exchange Server 2010
This type of message was send to all meeting participants, not just John Roberts. The meeting organizer was not Susan Smith. And the meeting organizer indicated that she didn't cancel the meeting.
Reviewing the message tracking logs indicated that a cancellation message for each participate was sent by Susan Smith. The message cancellation came from a Blackberry Z30 which uses ActiveSync.
It took a while to verify this, and was complicated by the fact that Susan Smith was not in the office to verify any information. We had also recently turned on the Calendar Repair Assistant and reviewed those logs to verify that it had not done this. We verified that the Calendar Repair Assistant had not processed Susan Smiths mailbox yet. We also verified that the repair performed for the meeting organizer didn't adjust this meeting.
Eventually, we found a Microsoft KB article that indicates some ActiveSync implementations have a flaw that allow attendees to become organizer of a meeting if they modify a meeting instance. The organizer isn't updated for other users, just the user with the ActiveSync device. The relevant text is this:
At this point, my best explanation is that the Z30 allowed Susan to become organizer. Then when Susan deleted a meeting which she would not be attending, the meeting was cancelled for all users. This fits our facts:
Issue 1.2 - An attendee becomes the meeting organizerWhen a user synchronize their iOS or Android device by using Exchange ActiveSync, they may unexpectedly become the organizer for a meeting to which they were invited. This does not change the meeting for all attendees.
This issue can occur if you change the reminder for a single occurrence of a recurring meeting on an iOS or Android device. There may be other changes to meeting items that cause the same problem.
Current issues (Exchange Online, Exchange 2016, Exchange 2013, Exchange 2010 and Exchange 2007)
Recent issues that have similar symptoms have been reported to Microsoft. These issues can affect users on all versions of Exchange Server. Currently, Microsoft cannot reduce the effect of these new issues. We encourage users to work with their device vendors to find a solution to the problem.
- Susan was the source of the cancellation
- Susan was using an ActiveSync device
- The email message indicated that the meeting was cancelled by the organizer