forwarding mail with same domain name

[liorz66]

Hi Everyone. i got an interesting problem i need help with.
thanks in advanced

Here’s my problem:
We’ve been aquired by a US company. We use Exchange2003 and they use some other mail (POP3). In order to use same mail domain @DOMAIN.NET I added recipient policy to the users and set it to be their default address, although we are not the MX or this domain. A public mail sent to localuser@domain.net is being forwarded by the other system (the official MX) to localuser@original-domain.com

All of the above works fine

UNTIL...

When my local user sends mail to US@domain.net (an existing recipient in US) I get NDR (I understand why...)
I need a solution for that situation.
I’ve tried creating a routing group and SMTP virtual server to forward the mail to their mail server but the NDR is generated before it reaches the Virtual Server.

Any suggestions will be blesses!

Thanks!
L