Message Not Delivered: Network issue caused a mail loop
The message could not be delivered because there was a network issue that caused a routing loop, causing this message to be forwarded over and over.
Double check the recipient's email address to make sure it is correct and attempt to resend the message.
If that does not work, consider contacting the recipient(s) through an alternative email address or other means.
5.4.6: Official Definition
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.
A routing loop caused the message to be forwarded too many times, either because of incorrect routing tables or a user- forwarding loop. This is useful only as a persistent transient error.