Transport

Exchange 2007 & 2010 use a different message routing design than Exchange 2003.  This is an important aspect to understand when transitioning from Exchange 2003 upwards due to the change in behaviour.

TechNet has articles that discuses these concepts :

Exchange 2010 http://technet.microsoft.com/en-us/library/aa998825.aspx

Exchange 2007 http://technet.microsoft.com/en-us/library/aa998825(EXCHG.80)… Read the rest “Exchange 2007 & 2010 Least Cost Routing”