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Token size affecting Free/Busy information between 2007 and 2010

I recently encountered an interesting issue with Token Sizes that I haven’t seen before with regards to Free/Busy information between Exchange 2007 and Exchange 2010 during an Intra-Org upgrade.
A little background on the environment, the customer I was working with was upgrading from Exchange 2007 to Exchange 2010 and had approximately 25,000 mailboxes.  There are also many nested Security Groups within the environment applied to user accounts primarily within the IT Department.  During the pilot phase with IT users, we had Exchange 2007 users reporting that Free/Busy information was not working for users whose mailboxes were moved to Exchange 2010.  What was strange was we were unable to reproduce the issue with test accounts or see any information logged in the Event Logs in either Exchange 2007 or 2010 after diagnostic logging was increased.
During further troubleshooting with the customer we stumbled upon the following KB article which describes the issue we were encountering:  After meeting with the customer’s Active Directory team, they stated that they recently had an issue with another application deployment where Token Size was impacting that project as well.  Since there are many documented Free/Busy issues with Exchange, this specific KB article did not initially come up in any online searches.
After following the steps outlined in Workaround section of the KB article, the Free/Busy issues were completely resolved.  A few items of note with the KB article, we did not run the PowerShell scripts specified in the article as there was no test environment to run these against before running them in production.  We also did not have to modify the Registry Keys on client workstations as the customer had already increased the MaxTokenSize due to an issue they had with another system.
I’ll be curious to see if this specific Free/Busy issue still occurs in Exchange 2013 with large environments upgrading from either Exchange 2007 or Exchange 2010.

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Trent Weiler

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