Message Not Delivered: Overloaded network
The message could not be delivered because the email system was unable to deliver the message due to recipient's email network being congested or overloaded.
Try waiting a bit since the mail server is busy. The sender's email provider will retry this message a few more times to see if the message gets through and provide further updates.
If this error continues, consider contacting the recipient through an alternative email address or other means.
5.4.5: 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.
The mail system was unable to deliver the message because the mail system was congested. This is useful only as a persistent transient error.