The following command line will provide you with a list of the Exchange 2007 send connector max send sizes:
get-sendconnector | list Identity,MaxMessageSize
The following command line will let you set the Exchange 2007 send connector settings:
set-sendconnector "[Connector Name]" -MaxMessageSize #MB
The following command line will provide you with a list of the Exchange 2007 receive connector max send sizes:
get-receiveconnector | list Identity,MaxMessageSize
The following command line will let you set the Exchange 2007 receive connector settings:
set-receiveconnector "[Connector Name]" -MaxMessageSize #MB
The following command line will provide you with a list of the Exchange 2007 transport information:
get-transportconfig
Microsoft site on managing size limits:
http://technet.microsoft.com/en-us/library/bb124345.aspx