When you introduce a the first Exchange Server 2007 server into an existing Exchange Server 2003 organization you may encounter an issue with mail flow between the two servers.
Emails sent from Exchange 2007 to Exchange 2003 work fine, however emails sent from Exchange 2003 to Exchange 2007 do not work and can be seen in the deferred delivery queue of the Exchange 2003 server.
This issue can be caused by the use of a smart host configured on the Default SMTP Virtual Server on the Exchange 2003 server.
To resolve the issue remove the smart host from the Default SMTP Virtual Server and instead configure a new SMTP Connector for the Routing Group to send internet email (the namespace of “*”) to the smart host.
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Thanks alott, I was experieencing this problem after exchange server 2007 installation, I am vegreatfull to you it realy solved my isuue, keep the good work continue
Thanks from an Exchange guy in Victoria. I already suspected it was that but it’s good to get confirmation before I do the configuration changes.