Delayed Message: Email routing issue due to network
The email message has not yet been delivered because network problems with the recipient's email provider limit routing this message.
Try waiting a bit since the receiving mail server is busy. Also, double check the recipient's email address when sending again.
If this error continues, consider contacting the recipient through an alternative email address or other means.
4.4.4: 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 mail system was unable to determine the next hop for the message because the necessary routing information was unavailable from the directory server. This is useful for both permanent and persistent transient errors. A DNS lookup returning only an SOA (Start of Administration) record for a domain name is one example of the unable to route error.