The MAIL$SEND_MESSAGE routine sends a message built with the
    MAIL$SEND_ADD_BODYPART routine to every user on the address
    list. If you have not used MAIL$SEND_ADD_BODYPART to construct
    a message, MAIL$SEND_MESSAGE sends only a message header.

    If MAIL$SEND_MESSAGE encounters errors sending to an addressee,
    it calls the routine specified by MAIL$_SEND_ERROR_ENTRY.
    Otherwise, it calls the routine specified by MAIL$_SEND_SUCCESS_
    ENTRY.

    If either routine is not specified, MAIL$SEND_MESSAGE calls no
    other routines.

    If you specify the MAIL$_SEND_RECIP_FOLDER item code, the mail
    is placed in the specified folder. Otherwise, the mail is sent to
    the default NEWMAIL folder.