CHECK <message-id>

    CHECK is used by a peer to discover if the article with the
    specified message-id should be sent to the server using the
    TAKETHIS command. The peer does not have to wait for a response
    from the server before sending the next command.

    From using the responses to the sequence of CHECK commands, a
    list of articles to be sent can be constructed for subsequent
    use by the TAKETHIS command.

    The use of the CHECK command for streaming is optional. Some
    implementations will directly use the TAKETHIS command and send all
    articles in the send queue on that peer for the server.

    On some implementations, the use of the CHECK command is not
    permitted when the server is in slave mode (via the SLAVE command).

    Responses that are of the form X3X must specify the message-id in
    the response.

1.1.2.  Responses

        238 no such article found, please send it to me
        400 not accepting articles
        431 try sending it again later
        438 already have it, please don't send it to me
        480 Transfer permission denied
        500 Command not understood