Control messages are a special kind of Usenet post that are used to control news servers. They differ from ordinary posts by a header field named Control. The body of the field contains control name and arguments.

There are two historical alternatives to header field Control. They are not supported by contemporary software and forbidden according to RFC 5537. However, the traditional format of the subject line is widely used in addition to the Control header: the subject line consists of the word "cmsg" followed by control name and arguments.

Read more about Cmsg:  Archiving

Other articles related to "cmsg":

Cmsg - Archiving
... Google Groups provides no means to read or write control messages ... It does not even execute cancels ...