Email problems

OK, I seriously am stumped right now. We have ISA 2004 running on a 2k3 box, we use exchange 2003 and everything is fully packed and up to date. Every now and then someone trying to send us mail gets an NDR telling them the message is refused and this is the error in our event log:

Event Type:      Warning
Event Source:      smtpsvc
Event Category:      None
Event ID:      4006
Date:            6/30/2005
Time:            3:31:22 PM
User:            N/A
Computer:      ISA01
Message delivery to the host '' failed while delivering to the remote domain '' for the following reason: The connection was dropped by the remote host.

For more information, see Help and Support Center at
0000: d3 02 04 c0               Ó..À    

I have been over our configurations time and time again and can't for the life of me figure out what is going on. We use a smart host and everything has been configured following Microsoft best practices. Any suggestions would be greatly appreciated.

Thank you very much in advance!!!

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Is the smart host yours or are you pointing to an ISP?
If the former can you do the latter?

The remote site is dropping your connection for some reason. Bit unkind not to generate an NDR though.
Usual reasons apply here, reverse lookup wrong, server announcing itself with an invalid email address etc.


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