Hi,

For those that are interested to see how Microsoft designed their internal Exchange 2010 deployment have a look at the whitepaper that just got published:

Exchange Server 2010 Design and Architecture at Microsoft
http://www.microsoft.com/downloads/details.aspx?FamilyID=accec9cd-9c09-4f7e-91c6-41f0e201b680&displayLang=en

Microsoft Information Technology (Microsoft IT) maintains a complex Microsoft® Exchange Server environment that consists of several geographic locations and multiple Active Directory® forests. There are 16 data centers, four of which host Exchange servers, to support more than 515 office locations in 102 countries with more than 180,000 users. These users include managers, employees, contractors, business partners, and vendors. Microsoft IT transitioned this environment to Exchange Server 2010 in less than seven months by taking advantage of its growing automation infrastructure and the enhanced deployment features available in Microsoft Exchange Server 2010, in combination with proven planning, design, and deployment methodologies.

This technical white paper discusses the Exchange Server 2010 architecture, design, and technologies that Microsoft IT chose for the corporate environment. This paper also discusses the strategies, procedures, successes, and practical experiences that Microsoft IT gained during the planning and design phase. Common planning and design tasks for many Exchange Server deployment projects include server design, high-availability implementation, and capacity planning. In addition to these tasks, transitioning a complex messaging environment to run on Exchange Server 2010 entails specific planning considerations regarding directory integration, routing topology, Internet connectivity, client access technologies, and unified messaging (UM).