The WebReady and Data Loss Prevention (DLP) features in Microsoft Exchange greatly increase the attack surface of an Exchange server. Specifically, Exchange running on Windows Server 2003 is particularly easy to exploit.
It's public knowledge that Microsoft Exchange uses Oracle Outside In. WebReady, which was introduced with Exchange 2007, provides document previews through the use of the Oracle Outside In library. Outside In can decode over 500 different file formats and has a history of multiple vulnerabilities. See CERT vulnerability notes VU#520721, VU#103425, VU#738961, and VU#118913.