"Larry Dighera" wrote in message
...

http://www.faqs.org/faqs/usenet/cancel-faq/part1/
"Cancel messages are sent out as a standard Usenet post, except
they contain a "Control: cancel message-ID" header. If a system
that accepts cancels receives the message, the post with the
specified message ID is deleted from that system.

Most major newsreaders allow readers to cancel their own posts
with a key press."

It may have escaped your notice, but most ISPs do not allow anyone to cancel
messages.