We have several 2000/2003 exchange servers in our organization on separate domains. We have been holding off on implementing a bridgehead server until 2007 was released. Now that it is out we would like to implement 2-2007 bridgehead servers (for fault tolerance). We will eventually upgrade our 2000 and 2003 servers and those server will assume the hub transport role for each domain, but the first step is to get a proper bridgeheads in place. The question is: can a 2007 edge transport server communicate with 2000/2003 servers without a hub transport server?
If this works our plan is to install two servers with Edge transport and then use connectors to have all of our exchange servers send/receive mail to those two servers. Using Address re-write we can maintain a unified look to all outgoing email. Because all of our separate domains are separate business units they can then choose to upgrade at their own schedule.