We have Google Apps for Business and are using it to replace our Exchange server. However, some of our users need to send more than 2000 messages a day sometimes. I wanted to have those few users continue to use the Exchange server for outgoing email. The problem with this is that if they send an email to another domain user, it will go to their domain Inbox rather than Google's. I am keeping their Exchange email accounts active as we migrate.
User 1 -> User 2: Goes to Exchange Inbox.
User 1 -> External User: Goes outside of the domain to the WAN.