Delayed Message: Message routed to non-email system
The email message has not yet been delivered because recipient's domain is not set up to handle email.
Check your recipient's domain in the recipient's email address for misspellings or missing letters. If an error is found, correct it in contacts list or address book for next time.
If necessary, contact the recipient another way (e.g., phone or text message) to confirm their email address.
4.1.9: 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 mailbox address specified was valid, but the message has been relayed to a system that does not speak this protocol; no further information can be provided.