If you want to configure the message size limits in Exchange 2010, there’s a few places to change this and that’s global settings as well as the connectors.
For modifying the global settings go to
Organization Configuration -> Hub Transport -> Global Settings ->Properties of Transport Settings
You can adjust your transport send/receive limits there.
Then you must modify the connectors found at
Organization Configuration -> Hub Transport -> Send Connectors -> Properties of Default Send
Here you can adjust your send connectors default maximum message size
Server Configuration->Hub Transport->Receive Connectors Pane->Properties of Default
Here you can adjust your receive connectors default maximum message size.