configure Postfix with one internal and external domain and setup like VPOP3

I have a scenario were the company has one branch. The main company is in London having a mail server with domain example.com. The branch office users in location India   were having problem sending and receiving mail from the main office it was very slow. To solve this issue the branch installed a new mail server with domain example.org and the mail forward was set in the main (example.com) mail server to forward the users of branch to user@example.org.  The branch users want to use example.com for sending and receiving in this case if a user sends a mail to another user in the branch office it has to go to main office mail server and forward to the branch mail server.  

I need to create a false domain in branch office mail server as example.com and if a local user in the branch sends a mail to local users in the same branch office the mail will be send locally without sending it out to main server. Also if a user sends a mail to main office users (users not in branch false domain) it might give unknown user error.
I need to try this in Redhat Linux using Postfix. I know there is a  program for windows called VPOP3 which can work..