Exchange 2007 / 2003 coexistance

I'm in the process of migrating from Exchange 2003 to Exchange 2007. There is currently one exchange 2003 and one exchange 2007 server up and running.  I can send email from Exchange 2007 to Exchange 2003 but I cannot do the reverse. The mail gets stuck in the "Messages Queued for deferred delivery" queue. I think this has something to do with the fact that I only have the Default SMTP Virutal Server, on the 2003 server, and it is set to use a smart host. This is so Message Labs can scan our outbound email.
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esmith69Connect With a Mentor Commented:
Yes that is correct.  I had a very similar issue that happened during a migration a few months ago.  You will need to remove that smart host from the 2003 server.

Before you do that though, on the Exchange 2007 server, I would configure a send connector and set it to route to your smart host.  The 2007 server should be smart enough to know not to use this connector for communication with the 2003 server.

To do this, open up EMC on the 2007 server and go to organization configuration->Hub Transport.  Go to the "Send Connectors" tab.  If there is nothing in the list, then you'll need to create a new Send Connector (something you would have needed to do eventually anyways).  If you're creating a new one, set its address space to *.  If it's an existing one, verify that this is already the case.  Then Under the properties for the send connector (either the new one or the existing one), under the "Network" tab, choose the option to route all email through a smart host.

Once you do that, you can change the 2003 server to NOT use a smart host and see if that fixes things.

I would also make sure you've followed all the steps listed in the following MS document ("How to Remove the Last Legacy Exchange Server from an Organizaton":

WeimanITAuthor Commented:
I followed your directions and then restarted they SMTP service on the Exchange 2003 Server. Now all the mail is routed correctly.
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