Further information needed on error message 5.7.1 Delivery not authorized, message refused

I am hoping to get some more information regarding the above error message.  I have a client who is having trouble sending emails to my Exchange 2003 server where we host the mail for company.com.

The MS Knowledge Base gives you this explanation:


But there really isn't an explanation (or more imporantly a solution or workaround) to the above error message.

What does this message mean that 'the remote domain has prohibited the sending domain from relaying'?  Why is relaying even involved, when it has reached it's final destination?

Some light on this for me would be appreciated.


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SembeeConnect With a Mentor Commented:
Could be generated by the ISP. Many ISPs now require authentication before they will allow email to be sent through their server. If they haven't authenticated when sending then that error would be generated.

Unless you have disabled anonymous access to your SMTP server this will not be a problem at your end.

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