SIGNALFILE <type> [path]<file>
        <type> =
            QNETSCAN   : QBBS-style netmail scanning index file.
            QECHOSCAN  : QBBS-style echomail scanning index file.
            NETSCAN    : Empty netmail scan file (for D'Bridge or FD).
            ECHOSCAN   : Empty echomail scan file (for D'Bridge).
            EXPORTLIST : Echoid-list of your new messages.
            IMPORTLIST : Echoid-list of new imported messages.

        This keyword defines some "semaphore" (signal) files, for use
        with some mailer/mail processing programs.