Question : Exchange 2007 Internal Sending Problems

We have an existing, working exchange 2000 server. We are implementing a new 2007 server to work with the 2000. We have a few mailboxes over on the 2007 server which work great for sending external mail. It does this using the SmartHostConnectorDelivery. But when I try to send internal mail, the messages get suck in queue (one called SMTPRELAYROTIRG). We get the error  "Primary target IP address responded with "451 5.7.3 Cannot achieve Exchange Server authentication."

Anyone have any idea why internal and external mail are using different delivery methods? The 2000 server should be sending the mail externally so 2007 is set to use a smarthost in the send connector.

I would appreciate any help, Im sorry the points are low but i only have 205 right now.

Answer : Exchange 2007 Internal Sending Problems

you dont want to use the smart host setting.... you should have an RGC that connect 2000 and 2007 which will be used to route mail between the 2 systems. 2007 will see the send connector and know to route the mail across the RGC to the 2000 smtp box then to the internet