Delayed Message: Message expired before delivery completed
The email message has not yet been delivered because the message was considered too old by the receiving system. It may have been delayed while being processed.
Double check the recipient's email address to make sure it is correct and resend the message.
If that does not work, consider contacting the recipient(s) through an alternative email address or other means.
4.4.7: 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 was considered too old by the rejecting system, either because it remained on that host too long or because the time-to-live value specified by the sender of the message was exceeded. If possible, the code for the actual problem found when delivery was attempted should be returned rather than this code.