rfc1036 December 1987

2.2.1.  Reply-To

    This line has the same format as "From".  If present, mailed replies
    to the author should be sent to the name given here.  Otherwise,
    replies are mailed to the name on the "From" line. (This does not
    prevent additional copies from being sent to recipients named by the
    replier, or on "To" or "Cc" lines.)  The full name may be optionally
    given, in parentheses, as in the "From" line.