https://en.wikipedia.org/wiki/List_of_SMTP_server_return_cod...
I imagine the "-5.7.1" is an in-house reference by the Virginia IT folks.
"Delivery not authorized, message refused" and "The sender is not authorized to send to the destination. This can be the result of per-host or per-recipient filtering. This memo does not discuss the merits of any such filtering, but provides a mechanism to report such. This is useful only as a permanent error."