In Exchange 2007 transport agents (e.g. RoutingAgents) were loaded and remained loaded until the transport service shutdown. In Exchange 2010 this behaviour seems to have changed so that agents are unloaded. I'm not sure what the criteria for unloading the agent are, but it seems to happen very rapidly and frequently even when there is activity in the SMTP transport.
Does any know if there a way to prevent agents from being unloaded? In Exchange 2003 there was an IEventIsCacheable interface that could be used to do this, but I can't find any equivalent interface or property in C# for Exchange 2010.