I have an interesting situation and really could benefit from some serious help.
I admin a 2008 R2 SP1 functional level forest, running a Exchange 2003 server (MAILMAN01) with 300 users mailboxes and 50 system/conference mailboxes. I have a brand new iSCSI SAN (10TB) on a gig-ethernet network, with 4-Dell R610's with 48GB of RAM-each connected to the SAN.
I plan to deploy Exchange 2010 to co-exist with the single, Exchange 2003 server indefinately (for legacy dependancy reasons, I cannot remove Exchange 2003). I have two Exchange 2010 enterprise licenses. The current smtp address (firstname.lastname@example.org) is what's bound to current Exch2003 organization, but the owners want to use a new smtp address (email@example.com) on the new Exchange 2010 environment.
Exchange 2010 will be virtualized ("virtually" no limit to guest configurations on memory and vCPU), and I need HA (failover, not load balancing) so I'm thinking about deploying two VMs where each is a combined role server (CAS, HUB & MBX) as part of a two-member DAG. The Exchange 2003 USER mailboxes only will be moved to the new Exchange 2010 server. However, the service accounts & conference room mailboxes will remain on MAILMAN.
Remember that mail coming to the smtp address firstname.lastname@example.org will continue to be routed to the Exchange 2003 server, while mail coming to email@example.com will be routed to the new Exchange 2010 architecture. These two Exchange platforms will be coexisting for the forseeable future.
Also, there is no DMZ to speak of. We have a nice-sized cluster of identical, firewall units that isolate us very well from the outside (save for what we allow in-and-out, of course). I want to employ two Edge servers as well. I realize that the Edge server is designed to be placed into a DMZ, but it can be made to work on the private network too. Do you see this as a benefit or a problem?
1) Is the design the most sensical route to take given the small size of my network and the fact that I need HA?
2) After the user mailboxes are moved from MAILMAN01 to the new Exchange 2010 server, how will the design allow for both SMTP addresses to receive and send email? In other words, how does my design support that and if it doesn't what's the best way to design this?
3) If my current design methodology is wrong, what would be a more efficient design to achieve the same goals? Will someone specify a better way to deploy this so that it meets the goals? Bear in mind that this is all in ESXi 5 hosts managed by vCenter/vSphere 5, by the way.
4) Does having the two, Edge servers provide additional HA benefit in the design?