This is a Delivery Status Notification (DSN).

I was unable to deliver your message to
fred34@gmail.com.

I said 
  (end of message)

And they gave me the error;
  550-5.7.26 Your email has been blocked because the sender is unauthenticated.
  550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM.
  550-5.7.26 
  550-5.7.26  Authentication results:
  550-5.7.26  DKIM = did not pass
  550-5.7.26  SPF [vger.kernel.org] with ip: [2001:470:1:191::d8da:d572] = did not
  550-5.7.26 pass
  550-5.7.26 
  550-5.7.26  For instructions on setting up authentication, go to
  550 5.7.26  https://support.google.com/mail/answer/81126#authentication 5a478bee46e88-2ed09f99823si2708379eec.2 - gsmtp