In a multi-tenanted Exchange 2010 installation is it possible to route to different send connectors for different organizations
Solution 1:
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!