We have set up a new exchange 2007 server in coexistance with exchange 2003, we can send emails from accounts on the 2007 server to accounts on 2003 but when we try to go the other way (2003 -> 2007) emails get stuck in the routing group que and whewn bounced you get this:

This message was rejected due to the current administrative policy by the destination server. Please retry at a later time. If that fails, contact your system administrator.

Is there anyone who has experenced this and has fixed it.. we spent all day yesterday googling the issue and nothing we found helped us...