Message Not Delivered: Message is too large
The message could not be delivered because the recipient's email provider has a message size limit and the message you sent is larger than what is allowed.
Check the body of the message for large amounts of text or for any large attachments. Try adjusting the text or reducing the size of attachments and resending.
Otherwise, contact the sender's email support team to see if they can help troubleshoot further.
5.3.4: 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.
The message is larger than per-message size limit. This limit may either be for physical or administrative reasons. This is useful only as a permanent error.