I currently have a very simple single server exchange 2003 setup.
I'm planning to add a single exchange 2010 server with all roles, and slowly move people over to it.
Technet and several blogs have plenty of guides to setting this up, but none of them seem to mention at which points in the setup there is downtime. Can I install and configure all the exchange 2010 roles on a new server without affecting the 2003 server?
At what point does external email HAVE to start going to the 2010 server instead of the 2003 server?