Delayed Message: Email content could not be accessed
The email message has not yet been delivered because an email system involved in transmitting the message had a problem accessing its content.
Try sending the message again in a while as this problem might be temporary or already in the process of being fixed.
If this error persists, contact the email provider for help.
4.6.6: Official Definition
A persistent transient failure is one in which the message as sent is valid, but persistence of some temporary condition has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful.
The message content could not be fetched from a remote system. This may be useful as a permanent or persistent temporary notification.