email from one domain not delivered

Hello
We recently set up an exchange 2003 server for a client. Everything seems to be working as expected, except there is one client that can not send email to the exchange server. THe client does not recieve an NDR or any error but the meaasge is not delivered to anyone in the domain. I have had the client send test messages to my personal account and these are recieved just fine. We are not using spam blocking for now until we get this issue fixed. and I have set IMF to 9. Is there any way to find out from the client why the message is not being delevered if an NDR/error is not generated? Any suggestions are welcome.

Thanks