Exchange: Users receive meeting invitation updates from declined instances

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After switching to Exchange 2016 a user of us received meeting invitations from another user for a reoccurring meeting, he already accepted. The invitation was for a single instance, the user had declined, and contained no additional information (like agenda, attachments, etc).

The sender was “Microsoft Outlook on behalf of ” and the body contained this message:

Exchange 2016 re-created a meeting that was missing from you calendar

(The same message appears on Exchange 2013: Exchange 2013 re-created a meeting that was missing from you calendar)

Additionally this messages were created each day at the same time (In our case 5:59 pm).

Possible Solution

After investigating the problem, we found a rather unknown feature (at least for us) in Exchange called “Calendar Repair Assistant”.

The CRA executes the following functions:

  • Detects inconsistencies
  • Determines if inconsistencies were intentional
  • Corrects inconsistencies
  • Sends a calendar repair update message if a correction was made

For more information, please read the technet article:
https://technet.microsoft.com/en-us/library/ee424432(v=exchg.141).aspx
This article is about Exchange 2010, but the functionality is the same for later versions of Exchange.

The last functions was the source of the new messages.

You can find the logs for the CRA in this folder (Exchange 2016):
<Exchange Installation Path>\v15\Logging\Calendar Repair Assistant

Depending on how annoying these mails are, you can disable the repairing of missing items via commandline:
Set-MailboxServer -Identity <Mailboxserver> -CalendarRepairMissingItemFixDisabled $true

A detailed describition of powershell commands can be found here:
https://technet.microsoft.com/en-us/library/ee633469(v=exchg.141).aspx

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