Delayed Message: Not authorized to send to mailing list
The email message has not yet been delivered because the recipient's email provider has blocked your email address from posting messages to this mailing list.
If it seems unlikely that your email address has been blocked intentionally, try sending the message again in a while in case this is a temporary problem.
Otherwise, contact the mailing list administrator.
4.7.2: 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 sender is not authorized to send a message to the intended mailing list. This is useful only as a permanent error.