Migrate E2K3 mailboxes to different E2K7 forest - Maintain different namespace like hosted

Trying to figure out the technical solution to the following:
1. Source forest (Exchange 2003) will be migrating only mailboxes to target Exchange 2007 forest
2. Namespace must be maintained
3. Quest tools will be used
4. OWA namespace must be maintained

Some questions I had were:
1. Should I standup new CAS servers in the target org?  Or can I pull this off with existing CAS servers (forget about performance for the time being) and URL creation?
2. Autodiscover will need to be configured for the "source namespace" in the target environment.  I am reading conflicting things on how to accomplish this.
3. Will upgrading the clients from Outlook 2003 to Outlook 2007 (in the source environment) gain me anything when it comes time to migrate to the target environment.
4. Separate issue, has anyone used TransVault to migrate away from EMCs EmaiXtender?
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kingofbytesConnect With a Mentor Author Commented:
Hi, thanks but I've got most of that covered....please see the "some questions I had were" section.

You can use the Move-Mailbox command. Here is a good tutorial on how to do cross-org mailbox moves: http://msexchangeteam.com/archive/2006/11/02/430289.aspx

Here is an article on how to setup a shared SMTP name space in Exchange 2007: http://www.msexchange.org/articles_tutorials/exchange-server-2007/planning-architecture/exchange-2007-smtp-namespace-sharing-different-relay-domain-types.html

After you set this up, you will need to change your MX records to point to the Exchange 2007 server.

To ensure mail flows properly after you migrate a user, you should create hidden contacts for all your mailboxes. Those contacts should have the SMTP address user@domaintarget.com. After you migrate a mailbox, set it to forward to the contact. This will ensure that users still on the Exchange 2003 server can send mail to users migrated to the Exchange 2007 server.
kingofbytesAuthor Commented:
delete question
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