I can send email from Exchange 2007. I can send and receive email between the two server (internal).I cannot send external emails from Exchange 2013. I get this 

Diagnostic information for administrators: 
Generating server: MBOX-1.xxx.xxx 
Receiving server: SRV-EXCHANGE.xxx.xxx (192.168.0.xx) 
xxx@gmail.com 
Remote Server at SRV-EXCHANGE.xxx.xxx (192.168.0.11) returned '400 4.4.7 Message delayed' 
6/9/2015 1:04:20 AM - Remote Server at SRV-EXCHANGE.xxx.xxx (192.168.0.11) returned '451 4.4.0 Primary target IP address responded with: "421 4.3.2 Service not available, closing transmission channel." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was 192.168.0.11:25' 

I have the Exchange 2007 allow the CAS IPs of Exchange 2013.

Is there a firewall between the two servers?  Are the two servers in the same Exchange organization?

Yes to firewall port 25 is open

Same Organization

Send connector in-place and configured properly on your Exchange 2013 server(s)?  Using a smarthost?  More information about your Exchange org is needed to offer suggestions.

Open all firewall ports between the two servers.  If it's a Cisco firewall, make sure "SMTP Fixup" and/or "Mailguard" is turned off.