This issue occurs in a race condition, in which a Microsoft Exchange ActiveSync mobile device that's in quarantine can synchronize emails to the Inbox folder in a Microsoft Exchange Server 2013 environment.
Note This issue doesn't affect other folders in the mailbox. When the device sends a <Sync> command without a corresponding <Change> command, the SyncState element will no longer let email messages be downloaded.
This issue occurs under the following conditions:
The ActiveSync mobile device is subject to quarantine.
The Allow/Block/Quarantine (ABQ) email messages that will be generally sent to the mailbox are deleted before the device synchronizes them.
The device sends a <Change> command on every synchronization request.
In this scenario, the <Change> command is allowed when the device is in quarantine, but it allows more than the bad ABQ emails to be downloaded.
To work around this issue, run the Remove-MobileDevice AffectedDeviceIdParameter cmdlet to remove the device from Exchange Server 2013 so that the SyncState element can be reset, and the device can resynchronize. This resolves the perpetual < Change> command.
To fix this issue, install Cumulative Update 11 or a later cumulative update for Exchange Server 2013.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.