I'm looking to convert from another emailenvironment to Exchange. We are looking at a single forest and two domains. I couldn't find any info on the impact of multiple domains on the Exchange Architecture. I'm looking at setting up two Exchange mailbox servers per domain. If I implement separate Hub, CAS and Edge servers and I want high availability, can any of these servers be set up handle the traffic for both domains (or to back up the other domain exchange server): In other words do I need 2 x MBX Servers Domain 1 2 x Hub Servers Domain 1 2 x CAS Servers Domain 1 2 x Edge Servers Doman 1 2 x MBX Servers Domain 2 2 x Hub Servers Domain 2 2 x CAS Servers Domain 2 2 x Edge Servers Domain 2 OR can I implement 2 x MBX Servers Domain 1 2 x MBX Servers Domain 2 2 x Hub Servers for Domain 1 and 2 2 x CAS Servers for Domain 1 and 2 2 x Edge Servers for Domain 1 and 2 Bill

Hi Bill, Actually you need at least a Hub server and a CAS server in the AD sites where you install Mailbox server roles. Introduction to Exchange 2007 Server Roles http://www.msexchange.org/tutorials/Introduction-Exchange-2007-Server-Roles.html If you are thinking about High Availability then you can look at below configuration. 1 CCR Domain1 2 nodes Mailbox server 1 NLB Cluster Domain1 2 nodes, on each CAS & Hub installed. 1 CCR Domain2 2 nodes Mailbox server 1 NLB Cluster Domain2 2 nodes, on each CAS & Hub installed. Edge Servers you can put as per your mail flow topology. References: http://exchangeserverinfo.com/2008/03/20/network-load-balance-for-hub--cas--exchange-2007.aspx http://msmvps.com/blogs/clusterhelp/archive/2007/10/05/exchange-server-2007-hub-transport-and-client-access-service-on-the-same-nlb-cluster.aspx http://technet.microsoft.com/en-us/library/bb123996(EXCHG.80).aspx