What to do after Remote-MoveRequest?

Hello all,

I would like to ask you the following:

Scenario: Exchange 2003 --> 2010 Inter Organization Migration.
@2003.com and @2010.com domains...

I have made a Remote MoveRequest in a test Mailbox, moving that from Exch2003 organization to the Exch2010 one...

My MX registries for @2003.com still continues pointing to the Exch2003 organization...

In Active Directory, the account for the migrated mailbox has turn into a "Mail Enabled User Account" and the Mailbox is completely moved to the Exch2010 Organization...

When a mail arrives, asking for this "user@2003.com", it receives a error message telling that the e-mail were not delivered.
The point is:
I cannot "forwarding" email using a mail enabled user. How can I forward the e-mail that arrives to this user to the new organization?

I've read about a contact to be created and used, but I don't understand how the contact and the mail enabled user will understand and see each other... :-(

Please light my way!!!