I have finalized all (6) of my supported ownCloud installations to work with Exchange 2010 via SMTP public address as well as via Exchange internal IP.
I needed to create an Exchange Relay Connector and specify the internal IP of the ownCloud Dev server. All authentication needs to be set as Anonymous for this connector.
Then, in the ownCloud admin section, specify the IP of the Exchange Server, or the public SMTP name, use your Exchange Server port (default for SMTP is 25), and select 'NONE' for authentication and 'NONE' for SSL / TLS.
You may also need to make sure the assigned email address is a legitimate one on the network.