The error "5.7.3 Client was not authenticated" indicates an issue with the Hub Transport Server.
Since the Hub Transport server is set for authentication out of the box, it was not designed to be outward facing towards the WAN. As a result, for Norman to deliver mail to a client with a Hub Transport server, you will need to set your Receive Connector to allow anonymous access.
The SMTP logs of a test message from Noman's delivery server to a Hub Transport server, which has not enabled anonymous access, will return the standard Client Not Authenticated message: “return-path address <email@example.com> rejected by mail.mydomain.com : 454 5.7.3 Client was not authenticated.”
To resolve this issue, please follow the steps below:
set-ReceiveConnector -identity “Default <SERVERNAME>″ -PermissionGroups AnonymousUsers