recipient primary SMTP address is missing or invalid>

I have exchange 2003 servers 2 exchange 2010 servers setup. All of the users are still on exch 2003 but when they send ceratin emails, they get bounce back messages that state the following:

The following recipient(s) could not be reached:

      Jim Smith on 9/6/2011 4:02 PM

            The message reached the recipient's e-mail system, but delivery was refused.  Attempt to resend the message.  If it still fails, contact your system administrator.

            <TMKEX01.test #5.2.0 smtp;550 5.2.0 RESOLVER.ADR.BadPrimary; recipient primary SMTP address is missing or invalid>

      Jane Doe on 9/6/2011 4:02 PM

            The message reached the recipient's e-mail system, but delivery was refused.  Attempt to resend the message.  If it still fails, contact your system administrator.

            <TMKEX01.test #5.2.0 smtp;550 5.2.0 RESOLVER.ADR.BadPrimary; recipient primary SMTP address is missing or invalid>


Is there something that I need to setup or change on the 2010 exchange server since the bounce back message is referring to the exch 2010 server, but as I mentioned, the users are still on exch 2003. They have not been migrated yet.