Be default, Exchange will not relay mail for anonymous users. This complicates sending mail from local appliances such as a PBX or copier.

Here we add a new Receive Connector “Local Relay” that permits a short list of devices (IP addresses) permitted to relay mail without authentication. If you add a new appliance that needs to send mail, do not configure SMTP Authentication. Add its IP address to the list of permitted devices instead.

Exchange Admin Center → Mail Flow → Receive Connectors

http://www.chicagotech.net/netforums/viewtopic.php?f=1&t=7156

By default, the Default Receive Connector will not relay mail for anonymous users or devices. They get an error like:

530 530 5.7.1 Client was not authenticated (state 13)

1. Go to Hub Transport under Server Configuration in Exchange Management Console.
2. On the Receive Connectors tab double-click the Default connector.
3. On the Permission Groups tab make sure that your Exchange Server has the following boxes checked:
   • Anonymous users
   • Exchange users
   • Exchange servers
4. On the Authentication tab, make sure that you uncheck the box under Basic Authentication that says “Offer Basic authentication only after starting TLS.”
5. Restart Hub Transport service.