Question : This system is configured to reject spoofed sender addresses

I got two offices such ABC.com and XYZ.com, we both using exchnage 2003 and WIndows 2003 enterprise server.

We can send and recieve message without any problem. The problem starts when we add the forwarder address for example Email send to user@abc.com, which has forwarder address in his account to user@xyz.com,

But user@abc.com can send email to user@xyz.com without any problem.

See below the error
ERROR.............................................................................

Your message did not reach some or all of the intended recipients.

      Subject:      test message 4
      Sent:      12/11/2008 10:57 AM

The following recipient(s) cannot be reached:

      User on 12/11/2008 10:59 AM
            The e-mail system was unable to deliver the message, but did not report a specific reason.  Check the address and try again.  If it still fails, contact your system administrator.
            < mail1a.optus.net.au #5.0.0 SMTP; 550 This system is configured to reject spoofed sender addresses>

Answer : This system is configured to reject spoofed sender addresses

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