The Usenet news protocol knows a special category of articles which evoke certain responses or actions by the news system. These are called control messages. They are recognized by the presence of a Control: field in the article header, which contains the name of the control operation to be performed. There are several types of them, all of which are handled by shell scripts located in /usr/lib/news/ctl.
Most of these will perform their action automatically at the time the article is processed by C News, without notifying the newsmaster. By default, only checkgroups messages will be handed to the newsmaster, but you may change this by editing the scripts.