I need to allow Microsoft Dynamics NAV to relay through our exchange server to send its purchase orders. I've configured the exchange servers SMTP Virtual Server to allow relaying from the NAV servers IP.
However it doesnt allow relaying to external addresses, if I try to send a purchase order to an internal address it works fine, if I try to send it to an external address I get "The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay for external address"
I've enabled diagnostic logging on the exhange server for SMTP events to go with the above message I get the following event
This is an SMTP protocol log for virtual server ID 1, connection #21. The client at "192.168.200.2" sent a "rcpt" command, and the SMTP server responded with "550 5.7.1 Unable to relay for ExternalAddress". The full command sent was "rcpt TO: <ExternalAddress>". This will probably cause the connection to fail.
Any ideas as to what is going on here.