We host mail for other organizations using a multi-tenanted Exchange 2010 installation.
We want to route to one of two different outbound relays based on which organization is sending the mail.
Is it possible to choose which send connector is used based on the organization?
Out of the box, the answer to this is no... although you can compile your own, or there are third party add-ons that will allow for sender-based routing.
Self-Compiled Example:
http://windowsshare.wordpress.com/2010/06/11/configure-sender-based-routing-in-exchange-2007
Third-Party:
http://www.messageconcept.net/en/products/exsbr/
http://ivasoft.com/routebysender.shtml
Hope that helps!