Office 365 Migration: StartMustExistCalendarCorruption

Gonthax used Ask the Experts™
I'm onboarding 250 mailboxes from a fully patched Exchange 2010 server to O365 and am trying to go for 0 bad items and I'm down to one last mailbox that I can't seem to fix.

A room mailbox with six errors with the following details:
  • Kind: CorruptItem
  • Scoring Classifications: Dumpster, Item, StartMustExistCalendarCorruption
  • Folder Name: Recoverable Items

The six errors actually seem to be only two bad items: The date and times match for three instances respectively and are from 2008.

I have run New-MailboxRepairRequest with all corruption types and nothing was found.

I did play around with Search-Mailbox but wasn't able to successfully track these instances down.

Any ideas on how I might track down the errors and remove them? I know I could simply set the bad item count to 6 here and move on but I'm a tryhard. :)

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Saif ShaikhServer engineer

Step 1: Download CalCheck from Microsoft
Get the 32 bit version the 64 bit is not really usable on all platforms.

Step 2: Extract the Zip
Find the download and extract the zip to a convenient location.
Run the CalCheck.exe application and choose the correct Outlook Profile to run the Calendar scan against.

Step 3: Check The Log Report
Open up the folder you extracted with CalCheck.exe in it and find the log file named CalCheck.txt
This will list all the calendar errors and specific references to why the errors will cause sync issues.
Give this to your end user or boss as evidence of the core issues

Step 4: Fix Errors
CalCheck will not delete any errors but it will report and move those errors to a new folder it creates in the users Mailbox called, you guess it, CalCheck.
You can force it to run the fix switch from the command line.
Windows key + R to get the Run dialoge
CD to the folder with CalCheck
C:\CalCheck_x86\CalCheck.exe -f
Choose the Outlook profile you want to run against and let it go. It will then scan, overwrite the log, create a CalCheck folder in the users mailbox and move any errored items over to that folder for delete or fix.
I also like to run this with the -r switch as it will create a report email and place it in the users inbox listing all the corruption for all to see.
C:\CalCheck_x86\CalCheck.exe -f -r
After the check is complete go back to the users Outlook and you will see a new CalCheck folder listed under the Mailbox.
Locate items that are unwanted and delete them
Recreate any appointments that have corruption and be sure to fill out all the info on the appointment form so as not to reintroduce the issue.


Thanks, Saif. I should have mentioned that I had also checked out CalCheck but in the interest of being thorough, I tried it again and it didn't find any corrupt items. I had to run the 64-bit version since I had 64-bit Outlook installed; the 32-bit version wouldn't find a mail app.

I do wonder if CalCheck also checks the Recoverable Items/Dumpster folders; I believe that's normally hidden but either way, I ran it with -f -r and it found no results. For the heck of it, I tried creating a new migration batch and it still failed with the 6 items. Welcome any other suggestions!
I just went ahead and upped the bad item limit to deal with the errors.

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