Question : send email through exchange 2003 during transistion to exchange 2007

I am currently upgrading our email system to Exchange 2007 from Exchange 2003.  I have it setup in a single server install in both instances.  I am able to communicate fine and send and receive email using the exchange 2007 server.  However, until I finish testing the installation of 07 I would like to have all my email sent through the 2003 server.  I am having problems with the reverse DNS failing from some external email servers if I send from the 2007 server since I have not switched the DNS to point to it yet.  I also do not want to switch the DNS yet since all the email mailboxes are located on 2003 still and switching the DNS in our case would mess up the outlook web access to those mailboxes.  So back to the original question, of how I can route the mail to leave the company using the exchange 2003 server?  Any help would be great.
Thanks

Answer : send email through exchange 2003 during transistion to exchange 2007

Not quite correct above.
If you want email to go through Exchange 2003 you need to create an SMTP Connector on Exchange 2003. Then set the Exchange 2003 as the bridgehead. Exchange 2007 will see that as a Send Connector that it cannot change.

The simple rule is to use the lowest version to manage during the transition phase. That ensures backwards compatibility.

Simon.