Message Not Delivered: Email servers are not communicating with each other
The message could not be delivered because the sending and receiving emaill systems had an issue processing the email. This is likely due to special characters (high ASCII) in an email address.
Check and the email address(es) of the recipient(s) for unusual characters. If an error is found, correct it in contacts list or address book for next time.
Otherwise, contact the sender's email support team to see if they can help troubleshoot further.
5.6.9: 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.
This indicates that transaction failed after the final "." of the DATA command.