In special cases, the list owner may set up the list to be message moderated. On a message moderated list, messages, instead of going directly to the list, are sent to one or more moderators. Moderators can accept or reject, but not modify the message. If the message is accepted, it is sent to the list unmodified. If it is rejected, it is e-mailed back to the sender, optionally with an explanation from the moderator.
On moderated lists it may take a little longer for the message to reach all the subscribers, since it has to be read and approved by at least one moderator before being sent out to the subscribers.