Question : Migrating from hosted Postfix to internal Exchange

We are trying to migrate off a hosted postfix based POP3 email provider to an internal Exchange 2007. We have changed our MX records to point to our hosted virus/spam scanning service, and they forward mail to our exchange server.
Our Exchange server is configured to deliver email locally when a mailbox exists, but to forward it to our old provider if not. I'm trying to get our POP3 provider to provide a similar service so that people not yet migrated over can still send email to already migrated users, but they are claiming ignorance or unwillingness for how to do this.

Any suggestions for postfix configuration to do this, or, if you think we're barking up the wrong tree with this suggestions for a cleaner way to migrate some, but not all users.

Answer : Migrating from hosted Postfix to internal Exchange

Your exchange server will need to have a different domain name (in addition to) your normal domain name.
say that you are [email protected] and [email protected], then you could create a new domain like [email protected]mple.com and setup the exchange server to accept mail for this in additon to the example.com. email.

On the postfix server in a file usually at /etc/postfix/virtual, you have a list of redirects like so...
[email protected]        [email protected]mple.com

Then in the transport file
exchange.example.com     smtp:[111.222.33.44]
so that postfix knows where to send mail for this new domain