Question : Can't send email to local Exchange server

Background to my problem:
One site (abc.com) is running a new Exchange 2007 server, the other (123.com) has an Exchange 2003 server.  We have been able to email back and forth with no problems.  On Thursday we connected both sites with a point-to-point T1.  Since then 123.com can email to abc.com, but abc.com can't email to 123.com.  Emails stay in Exchange 2007 queue with Last Error - 451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to connect."
In the SMTPSend log, I see:
172.16.40.2:25,*,,"Failed to connect. Error Code: 10061
this refers to the subnet the 123.com server is on but it is 172.16.40.4.  Not sure why it is trying to connect to 172.16.40.2.
Any help would be greatly appreciated.

Answer : Can't send email to local Exchange server

I get the same results as the previous nslookup.

But, I think I have the issue resolved.  I created a Send Connector on the Exchange 2007 server for 123.com and pointed it to 172.16.40.4.  Mail did go through.