Currently we have Postfix mail server, responsible for myorg.lt domain (holds mx record). It uses Transport mapping to sync with our AD (ldap protocol), and creates smtp records for email@example.com smtp=192.168.0.5 (Exchange 2003 srvA). In this way postfix knows, when to send mail to internal Exchange organization, when to generate NDR. It has pop3 mailboxes for myorg.lt domain too.
Exchange 2003 srvA has one smtp connector to route all outgoing mail to ISP SMTP server, and routing group connector to route *@myorg.lt to Exchange 2003 srvB, witch is located in other routing group. Exchange 2003 srvB has one smtp connector, sending all outgoing mail to ISP smtp server.
We are planning to implement Exchange 2007 server, with Exchange 2007 Edge server.
Main objective is to make new Exchange 2007 resposible for myorg.lt domain, so edge server gets all antispam work.
In Exchange 2007 i will make Internal relay domain for myorg.lt domain, and route all @myorg.lt mail to postfix server.
The problem as i see will be linux sending NDR for users that are in Exchange 2007 organization. No ldap or other connections with Exchange 2007 AD will be created for linux.
In later steps we plan to decomission postfix linux server (now it has too many pop3 mailboxes) and Exchange 2003 srvA .
Anyone can help with routing ? :)