I work for a school district that is considering going with inhouse Exchange vs the web solution we currently use for Staff email. Our AD consists of 1 domain and 5 sites. We would have about 500 total users, but some sites a couple of the sites could have as little as 20 users at them. Is it absolutely necessary to have an exchange server at each site housing mailboxes, clientaccess, and hub transport? That seems like so much unnecessary hardware. We would be using OWA only because we actually have many users using Apples. It seems like I could run 1 server with mailboxes, client access, and hub transport and be done with it. I know that I would need redundancy and such. Having to buy another server for each building isn't for condusive for a public school district.

You're misinterpreting the design guides. Designcan easily accomodate a single centralized deployment, regardless of how many Physical/Active Directory sites you have. Erik