Mails are not delivered to the exchange server.
The Appliance livelog shows the message: 452 4.3.1 insufficient system resources.
This message is reported from exchange to the appliance and means, that the exchange server lacks resources to accept mail.
This error cannot be solved with the REDDOXX appliance. Following microsoft article might help:
http://technet.microsoft.com/en-en/library/bb201658