The following non-delivery report:
is generated when sender's IP address is on McAfee's internal IP reputation (IPR) list.
This might be caused by high spam traffic from the IP passing through McAfee filters. The IP is usually cleared automatically after 30 minutes if spam traffic stops.
Resending the message might also work right away if the message goes through a different server chosen randomly. However, it is recommended to wait for at least 30 minutes before attempting to send the message again.