I am in the middle of a migration from Exchange 07 to 2013. I have installed 2013 and just moved my first TEST user. I do not have my SSL certificate yet, so I am testing via 2013 OWA.
From the 2013 Test Account I can successfully send mail outside the organization & receive the reply, BUT I cannot send mail internally to ANY of the users residing on the Exchange 07 server.
If I send mail from an existing user on the 2007 server to the TEST account residing on the 2013 server it is successful.
What am I missing? Why can I not send mail internally from 2013 to 2007?