I know a few people who are getting ready for an E2k3 upgrade and thought they might enjoy this link.
This guide is designed to provide you with essential information about how to harden your Microsoft® Exchange Server 2003 environment. In addition to practical, hands-on configuration recommendations, this guide includes strategies for combating spam, viruses, and other external threats to your Exchange 2003 messaging system. While most server administrators can benefit from reading this guide, it is designed to produce maximum benefits for administrators responsible for Exchange messaging, both at the mailbox and architect levels. This guide is a companion to the Windows Server 2003 Security Guide . Specifically, many of the procedures in this guide are related directly to security recommendations introduced in the Windows Server 2003 Security Guide. Therefore, before you perform the procedures presented in this guide, it is recommended that you first read the Windows Server 2003 Security Guide.