Cannot send mail from Exchange 2013 to Exchange 2007

I have anExchange 2007server withallroles on thesame server.Ihave now installedtwoExchange2013serverswith both with CASandMBXroles.There is also aDAGbetweenthe new servers.AllmailgoesthroughaBorderWarebesidesthe internalmail.

Ican send mailfromboth environmentsto the Internet.I canalsosend internalmail fromExchange 2007to Exchange 2013.But the problemis that I am unable tosendfromExchange 2007to Exchange2013.I'vedebugged,but notsolved the problem andthere are fewarticleson the Internet.

Any suggestions?