Unable to send and receive emails internally after exchange 2013 introduced in exchange 2007 environment- coexist environment

Hi All

we have exchange 2007 (2HT,2CAS,3 MBX in CCR and SCR) and introduced exchange 2013 6mbx,3 CAS  recently.

all the URL's are currently pointing to exchange 2007, SSL certificates are installed in all the CAS servers, created 30 new DB's in ex2013 and disabled 6 default mailboxes in 2013.

we did not add mbx servers in sendconnector, policies are not migrated, no configuration has done

Issue: 2013mbx test1 to mbx tes2 is working but mailflow from 2007 to 2013 and 2013 to 2007 is not happenings,

Please guide me or Point me to a Correct KB artical about the configuration. (how will i establish or configure the communication between internal versions)

i assume it has to be communicated internally without any configuration