Shared NameSpace between Exchange 2003 and Exchange 2013

Hello, 

We have Exchange 2003 . We have exchange 2013 in another AD domain. We want to configure Shared NameSpace between two exchange Servers. I have cofnigured on Exchange 2013 side using send connectors. 

I want to configure email flow like this. 

between exchange 2013 and Exchange 2003. 

If send emails from Exchange 2013 user to Internet, should go via 2003 to internet.. 

What should i configure on Exchange 2003  ? 

regards