rfc1036 December 1987

3.1.  Cancel

           cancel <Message-ID>


    If a message with the given Message-ID is present on the local
    system, the message is cancelled.  This mechanism allows a user to
    cancel a message after the message has been distributed over the
    network.

    If the system is unable to cancel the message as requested, it
    should not forward the cancellation request to its neighbor systems.

    Only the author of the message or the local news administrator is
    allowed to send this message.  The verified sender of a message is
    the "Sender" line, or if no "Sender" line is present, the "From"
    line.  The verified sender of the cancel message must be the same as
    either the "Sender" or "From" field of the original message.  A
    verified sender in the cancel message is allowed to match an
    unverified "From" in the original message.