Exchange Troubleshooting EventID 9646: MAPI session exceeded the maximum of 500 objects of type “objtFolderView"

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On Exchange you might see the following error logged, event ID 9646.  This error is caused by a users mailbox having over 500 folders and sub-folders. Here is the event log:

http://collaborationpro.com/wp-content/uploads/2015/02/event-id-9646-300x208.png

Solution:

To resolve this issue create the following registry keys on each of your mailbox servers:

  • Navigate to HKLM > System > CurrentControlSet > Services > MSExchangeIS > ParametersSystem.
  • Create a new key in ParametersSystem named MaxObjsPerMapiSession.
  • In MaxObjsPerMapiSession, create a DWORD named objtFolder with a decimal value of 600.
  • Create a second DWORD named objtFolderView also with a decimal value of 600.

No need to reboot the Informational Store. It will pick up the changes after a few minutes.

You may still see this error, only this time specifying that the user has exceeded the new 600 object threshold. In which case increase the value of each DWORD by 100 and repeat until the errors stop.

Other Resources

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