Message Not Delivered: Message authentication issues
The message could not be delivered because the email sending system uses DKIM, an authentication mechanism. Either the sending or receiving email system had some problem with the sending system's DKIM.
Retry the email message see if it was a one-time problem or if the same error occurs.
If the problem continues, contact the sender's email support team to help identify any misconfiguration with the sender's account or with the email system. In particular, issues with the use of email authenticaton such as DKIM should be investigated.
5.7.5: 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 transport system otherwise authorized to validate or decrypt a message in transport was unable to do so because necessary information such as key was not available or such information was invalid.