gnus: Canceling and Superseding

 
 3.5.4 Canceling Articles
 ------------------------
 
 Have you ever written something, and then decided that you really,
 really, really wish you hadn’t posted that?
 
    Well, you can’t cancel mail, but you can cancel posts.
 
    Find the article you wish to cancel (you can only cancel your own
 articles, so don’t try any funny stuff).  Then press ‘C’ or ‘S c’
 (‘gnus-summary-cancel-article’).  Your article will be canceled—machines
 all over the world will be deleting your article.  This command uses the
 process/prefix convention (SeeProcess/Prefix).
 
    Be aware, however, that not all sites honor cancels, so your article
 may live on here and there, while most sites will delete the article in
 question.
 
    Gnus will use the “current” select method when canceling.  If you
 want to use the standard posting method, use the ‘a’ symbolic prefix
 (SeeSymbolic Prefixes).
 
    Gnus ensures that only you can cancel your own messages using a
 ‘Cancel-Lock’ header (SeeCanceling News (message)Canceling News.).
 
    If you discover that you have made some mistakes and want to do some
 corrections, you can post a “superseding” article that will replace your
 original article.
 
    Go to the original article and press ‘S s’
 (‘gnus-summary-supersede-article’).  You will be put in a buffer where
 you can edit the article all you want before sending it off the usual
 way.
 
    The same goes for superseding as for canceling, only more so: Some
 sites do not honor superseding.  On those sites, it will appear that you
 have posted almost the same article twice.
 
    If you have just posted the article, and change your mind right away,
 there is a trick you can use to cancel/supersede the article without
 waiting for the article to appear on your site first.  You simply return
 to the post buffer (which is called ‘*sent ...*’).  There you will find
 the article you just posted, with all the headers intact.  Change the
 ‘Message-ID’ header to a ‘Cancel’ or ‘Supersedes’ header by substituting
 one of those words for the word ‘Message-ID’.  Then just press ‘C-c C-c’
 to send the article as you would do normally.  The previous article will
 be canceled/superseded.
 
    Just remember, kids: There is no ’c’ in ’supersede’.