New Exchange 2003 server not receiving outside emails

I installed a new Exchange 2003 server and moved just a couple of mailboxes.
Here is the issue.  
I can email to recipients on the old Exchange server from the new one but I cannot receive mail from mailboxes existing on the old server to the new Exchange server.
I would like to correct this so I can move a few mailboxes at a time instead of moving everyone at once.  

Two servers
MX1 (OLD) and MX3 (NEW)
MX3 can email to MX1 mailboxes but MX1 mailboxes cannot email to MX3 mailboxes.  NO NDR at this time.
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SembeeConnect With a Mentor Commented:
The number one reason for this is a smart host on the SMTP virtual server on the original machine. Check that first. If there is a smart host, remove it and replace it with an SMTP Connector.

The next most frequent reason is AV software blocking the smtp traffic.
Check whether that is happening.

Ensure that you can telnet to port 25 of the other machine using all three combinations:

telnet 25
telnet servername 25
telnet 25

Try sending a test email from MX1 to MX3 using Telnet:
mcrosslandAuthor Commented:
Your right on the money once again!  It was the smart host.

Have a great day!
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