Just before Exchange 2007 takes the spotlight, Microsoft does not leave its current version unattended and publishes and updates its (really useful) guides.
Microsoft Exchange Server 2003 Technical Reference Guide
This guide is for Exchange Server experts who require detailed information about the architecture and interaction among core components of Microsoft Exchange Server 2003.
Microsoft Exchange Server 2003 Security Hardening Guide
This guide is designed to provide you with essential information about how to harden your Microsoft Exchange Server 2003 environment.
Working with Active Directory Permissions in Microsoft Exchange Server 2003
This guide discusses the necessary minimum rights needed for Exchange administrators to manage Exchange-related data in Active Directory as it pertains to user, inetOrgPerson, group, and contact objects so that separation of administrative tasks can be implemented.
Microsoft Exchange Server 2003 Performance and Scalability Guide
This guide provides information about Microsoft Exchange Server 2003 performance and scalability.
Microsoft Exchange Server 2003 Message Security Guide
This guide discusses how, when using S/MIME, encryption protects the contents of e-mail messages and digital signatures verify the identity of a purported sender of an e-mail message.
Microsoft Exchange Server 2003 Transport and Routing Guide
This guide explains how transport and routing works in Microsoft® Exchange Server 2003, and how you can configure Exchange to enable internal and external mail flow.
Working with Microsoft Exchange Server 2003 Stores
The Microsoft® Exchange Server 2003 store is a storage platform that provides a single repository in which you can manage multiple types of unstructured information. This guide provides in-depth information to make administration and troubleshooting tasks easier for you to perform.