Can someone please explain to me how to setup co-existence when there are two email servers? I am not asking for all the specifics. Just summarize the steps. Also, I do not want references to 3rd party tools. Instead, here is the scenario:
The Domino server is the main server, and this is where the MX record points to. The goal is to begin using Exchange 2010. People will have their messages migrated in stages. So, some people will be in Domino and some people will be in Exchange.
When a person is migrated to Exchange, I want their messages "relayed" to the Exchange server. So, I want people in the Domino side to be able to send messages internally and to the people in the Exchange server. Similarly, I want people in the Exchange side to be able to send messages internally and to people in the Domino server.
The email address for all users will remain the same except for a small few.
In a scenario like this, how can I setup co-existence so that everyone gets their messages regardless of the system they are in?