We are looking at upgrading our Exchange Server 2003 environment to 2010. My question is about the design. We have the opportunity to build the 2010 environment from the ground up. As I understand it the CAS is a huge portion of how the servers now interact. We have approximately 6200 active users and we would like the optimal/minimal design for a single site environment. We currently have 5 ADs that will be upgraded with the new schema (including legacy permissions) prior to the full upgrade.
How many CAS servers would we need versus the other roles?
We're using a VM environment and we want to finish the environment, test move a few mailboxes to validate and eventually move all the mailboxes and just turn the old environment off completely.