I want to starta small group (no more than 15 people) on Exchange 2007 with coexistence of Exchange 2003. My plan is to install the Cal/Hub/Mail/UM all on one server. Now I have read that installing Cal should be first cause people on 2k7 would not be allowed to access OWA via 2k3. So I have a few questions that I am looking for some clear answers on. 1. If I add the new 2k7 server, will my old 2k3 OWA server go away? 2. Regarding Routing, I have read that when you install 2k7 it asks for a Bridge Head Server in 2k3. Will the 2k7 be the main bridge head server or will the 2k3 still be the bridge head and anything headed for 2k7 will be passed via the SMTP connector? Or will I need to change my DMZ mail server to point to the new 2k7 server to route mail in the domain? Internet --->DMZ Mail Server ----> 2k3 Bridge Head ----> 2k3 Mail | ----->2k7 Server Hope this all makes sense.

On my second question, I think alot is answered here http://msexchangeteam.com/archive/2006/11/17/431555.aspx

First of all, if you plan to use UM with SP1, it'll need a dedicated server. Sorry. e2k3 users can hit OWA through 2007 CAS no problem because in 2003 OWA is actually rendered by the backend server. The users will see the 2007 logon page, but then the 2003 OWA.

Do you know UM and SP1 have to be on dedicated server? As far as the OWA goes, in answering my question I would just change the dns to point to the CAL server of 2k7 and I could take down my old 2k3 front end server. But then that leads to the question, how does that play well with the whole RPC over HTTPS for 2k3?

UM with SP1 has to be on dedicated hardware. Check out the SP1 release notes. As far as RPC over HTTPS as long as you install RPC proxy and enable "Oultook Anywhere" on the CAS server it'll work fine with the 2003 clients.

Well that just bites! Thanks for the heads up on that.