X.400 Bridgehead for Microsoft Exchange is a new product from Isode partner Boldon James, produced in collaboration with Isode. It's primary goal is to provide X.400 protocol connectivity for Microsoft Exchange 2007; this capability was provided as a part of Exchange 2003 and earlier versions, but is not included with Exchange 2007.
In a new whitepaper now available from the Isode website, X.400 Bridgehead for Microsoft Exchange - Technical Architecture and Back-end Features, we describe the architecture of X.400 Bridgehead, and summarize it's key features. It is particularly oriented towards understanding the capabilities of X.400 Bridgehead in the context of older versions of Exchange and full X.400 Message Transfer Agents (MTAs).
The whitepaper which, like all Isode whitepapers, is free and can be viewed without registration, is available here.