SMTPD II
    Patterns in src, from
        ALL
        KNOWN|UNKNOWN
        NS=
        USER - in from - match in identd
    Examples
        deny:UNKNOWN:AL::ALL
        deny:*.spamhaus.com *.junkmail.com:ALL:ALL
        noto:ALL:ALL:*%*@*:551 Sorry %H (%I), I don't allow relaying to %T
        noto:RBL.rbl.maps.vix.com:ALL:ALL:550 Mail from %I in MAPS RBL being blocked, see http%C//maps.vix.com/rbl/
    Reference
        man smtpd, smtpfwdd
        Commented examples in /usr/share/smtpd