In our situation, after a mailbox migration from one database to another database, the mailbox was flagged as quarantined by Exchange.  This looks to be a feature added in Exchange 2010 to prevent a single mailbox from taking down the entire information store.

To verify the mailbox is quarantined you can check the registry on the Exchange server.

Get-MailboxStatistics – Identity user | fl IsQuarantined


HKLM\SYSTEM\CCS\Services\MSexchangeIS\Servername\Private-dbguid\Quarantined Mailboxes\ {Mailbox GUID}


To get the Mailbox GUID

Get-MailboxStatistics – Identity user | fl

To get the Database GUID

Get-MailboxDatabase -Identity database | fl guid


Reset the quarantined mailbox by deleting the quarantine registry key for that mailbox.

The database has to be dismounted and remounted OR the Exchange Information Store service needs to be restarted for the change to take effect immediately.  If the error still exists, the mailbox could crash the store and become quarantined again.