Lookup for "214 2.7.2"
This status code indicates a successful delivery or other operation. Any details are simply notes.
Basic Status Code Details (214)
Help message [Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user]
Enhanced Status Code Details (2.7.2)
Mailing list expansion prohibited
The sender is not authorized to send a message to the intended mailing list. This is useful only as a permanent error.