On an Exchange 2010 environment that has some Exchange 2003 servers still in the site, is it possible to send all mail originating from users with *@mydomain.tld to a specific pair of smart hosts? If so, how?

See this - http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/d0859d7e-1855-4ada-a63a-9c678d84e6b9 If you still have Exch 2003 around, your users are in 2003, then you can place delivery restriciton on the SMTP connector. If you users are on 2010, then see the link.Sukh

I created the new send connector. The scope is *.mydomain.tld. When I send mail it does not route through the smart host. It simply goes out my existing Internet connector. Do I need to cycle some service? The domain "mydomain.tld" represents an SMTP domain on my Exchange server. I believe what I'm trying to do is considered a form of sender based routing? Or domain based routing? I want to end up with: mydomain.tld -> smarthost1.tld mydomain2.tld -> no smarthost mydomain3.tld -> smarthost3.tld etc.

I created the new send connector. The scope is *.mydomain.tld. When I send mail it does not route through the smart host. It simply goes out my existing Internet connector. Do I need to cycle some service? The domain "mydomain.tld" represents an SMTP domain on my Exchange server. I believe what I'm trying to do is considered a form of sender based routing? Or domain based routing? I want to end up with: mydomain.tld -> smarthost1.tld mydomain2.tld -> no smarthost mydomain3.tld -> smarthost3.tld etc. You can't do that with Exch 2010, see the link I posted. Alternative is 3rd part app or a custom agent.Sukh

Use a 3rd party product: http://ivasoft.com/routebysender.shtml