Exchange Server 2007 Protocol Documentation
Following the commitment that Microsoft made in order to open most of its protocols, "so that software developers, business partners and competitors can better interact with these Microsoft products or invent new solutions for customers", the Exchange Server 2007 Protocol Documentation is now available to download.
The Microsoft Exchange Server 2007 Protocol technical documentation set provides detailed technical specifications for Microsoft protocols and extensions to industry-standard or other published protocols that are implemented and used in Microsoft Exchange Server 2007 to interoperate or communicate natively with Microsoft Office client and other server products.
The documentation set includes a set of companion overview and reference documents that supplement the technical specifications with conceptual background, overviews of inter-protocol relationships and interactions, and technical reference information.
If you can't spare the extra 45MB, this information is also available online at the MSDN site.