530 5.7.1 Client was not authenticated - Exchange 2010

I finally got the MX record to publish for one of my two test external domains. Then I tried to send a test email, but got rejected with the error, "530 5.7.1 Client was not authenticated". Fortunately, it didn't take long to find the fix.

1. Go to Exchange Management Console


2. Go to Server configuration, hub transport server and default receive connector's properties


3. Click on last tab “permission Groups” and tick a check mark into “Anonymous users” click apply and ok.

Thanks for this article, http://smtp25.blogspot.com/2009/04/530-571-client-was-not-authenticated.html.