The Jargon File (version 4.4.7, 29 Dec 2003):

bottom-post
 v.

    In a news or mail reply, to put the response to a news or email message
    after the quoted content from the parent message. This is correct form, and
    until around 2000 was so universal on the Internet that neither the term
    ?bottom-post? nor its antonym top-post existed. Hackers consider that the
    best practice is actually to excerpt only the relevent portions of the
    parent message, then intersperse the poster's response in such a way that
    each section of response appears directly after the excerpt it applies to.
    This reduces message bulk, keeps thread content in a logical order, and
    facilitates reading.