Why do I get a NDR 5.7.1. Relay Access Denied message when replying to an email? It does not happen all the time, only to some messages and is totally random.
My environment is Exchange 2003 Std on Windows 2003 Std. Their environment is SBS 2003, whcih I manage!
Is it down to 3 MX records - primary pointing directly to their own server and 2 additional ones pointing to ISP's Mail Servers?
I am assuming the NDR messages are hitting the ISP mail servers and getting rejected. Is this right?