Control messages are used for communication among USENET host machines, not to be read by users. Control messages are distributed by the same newsgroup mechanism as ordinary messages. The body of the Control header line is the message to the host. For upward compatibility, messages that match the newsgroup pattern “all.all.ctl” should also be interpreted as control messages. If no Control: header is present on such messages, the subject is used as the control message.
You can cancel a Usenet message after you send it, but that doesn’t guarantee it won’t get archived first.
You might sometimes post a message and then wish to cancel it, either because the message contained incorrect information, or because you regretted what you posted. Of course, the best recommended protection against this is to reread everything before you post it to the Internet and ask yourself if you’re sure you want to send it out to the entire world.
However, if you do send a post and wish to cancel it, you can send another post to the same newsgroup with a “control” header that specifies a “cancel” command along with the <message-ID> on the message you want to cancel. Most news readers contain a built-in menu command to cancel a posting. For example, on Netscape, highlight the article, and then select the menu item “Edit / Cancel” which will display the following.
Control: cancel <message-ID>
The cancel message will first be sent to your local news server, which will delete the message from their server right away, and then send the command to all other news servers to which it sent the message in the first place, so that it will be removed at about the same speed that it was posted.
However, remember that there is no guarantee that someone won’t read your message before it is canceled, especially if the cancel is sent several minutes after the original message. Also, there is no guarantee that it will be canceled before some newsgroup archive picks it up and stores it in their database.