I'm in the process of moving two law firms to hosted Exchange 2007, a service that the consulting company I work for offers. Let's call these two firms Crane Law and Poole Law. These two firms were ONE firm just six months ago, but split. So they have three email domains:

Old Firm: craneandpoole.com New Firm 1: cranelaw.com New Firm 2: poolelaw.com

Both Firm 1 & Firm 2 use craneandpoole.com email addresses, as for the other two domains, only people who work at the respective firm use that firm's domain name, natch.

Currently these two firms are still using the same pre-split internal Exchange 2007 server, where MX records for all three domains point.

Here's the problem. I'm not moving both companies at the same time. I'm moving Crane Law two weeks before Poole Law. During this two weeks, both companies need to be able to:

1. Continue to receive emails addressed to craneandpoole.com
2. Send emails between firms, using cranelaw.com and poolelaw.com accounts

I also have a third problem:

1. I'd like to setup all three domains in my hosting infrastructure way ahead of time, to make my own life easier

What would solve all my problems would be, if there is some way I can tell Exchange 2007, even though this domain exists locally forward on the message to the outside world using public MX record as a basis for where to send it (or if I could somehow create a route for it statically that would work too).

If this doesn't work, to address points #1 when I migrate Crane Law, I will delete all references locally to cranelaw.com on their current Exchange server, and setup individual forwards for each of their craneandpool.com mailboxes to forward to our hosted exchange server. This will also take care of point #2, since the cranelaw.com won't be there locally, when poolelaw.com tries to send to cranelaw.com, public MX records will be used for mail routing decisions and go to my hosted exchange. The bummer of that though is, I won't be able to setup poolelaw.com ahead of time in hosted Exchange, will have to wait to do it day of :(

Sorry for the long and confusing post. Just wondering if there is a better or simpler way to do what I want? Three tier forests and that kind of thing are out, this is just a two week window where they won't be in the same place.