Redirect local domain mail externally (Exchange)

[ptaylor965]

Hi,
Please note: The question is at the bottom of the post

Background:
The e-mail server is exchange 2007 server.

I have a customer that has requested that we host a push mail account for two of his mail accounts.

We did this by creating an account on our domain and forwarding all mail from their two accounts to our domain.

This works well. Every time a message is sent to their main address ([e-mail]) the mail is redirected to our server too ([e-mail])

This allows them to use their PCs to access their mail from their mails server and their Windows Mobile phones to get the mail pushed from our server.

The problem:
If they send mail from their phones it goes out from [e-mail].
Adding [e-mail] to their account as the default outgoing address fixed this BUT if user1 emails user2 from the phones the mail is not delivered to the [e-mail] address but only delivered to the local address [e-mail]

The Question
Can this be stopped so that all mail from these users is sent out of our server?