Message Not Delivered: Not authorized to send to mailing list
The message could not be delivered because the recipient's email provider has blocked the sender's email address from posting messages to this mailing list to which the message was addressed.
Fixes
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.
5.7.2: Official Definition
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 5.X.X:
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.7.2:
The sender is not authorized to send a message to the intended mailing list. This is useful only as a permanent error.