Delayed Message: Email servers are not communicating with each other
The email message has not yet been delivered because the sending and receiving emaill systems had an issue processing the email. This is likely due to special characters (high ASCII) in an email address.
Check and the email address(es) of the recipient(s) for unusual characters. If an error is found, correct it in contacts list or address book for next time.
Otherwise, contact the sender's email support team to see if they can help troubleshoot further.
4.6.9: 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.
This indicates that transaction failed after the final "." of the DATA command.