Hi,
'relaying denied' is (usually) sent from an MTA when it is not the final destination for the domain of the email being sent, and does not have any policies in place to forward the message on to its final destination.
The fact that this was a DCID ( delivery connection ) implies that the IronPort was attempting to send a message to Exchange/Notes/etc.. and that server responded that it could not process email for the domain in question.
-whardison