    public function mail($from)
    {
        $useVerp = ($this->do_verp ? ' XVERP' : '');
        return $this->sendCommand(
            'MAIL FROM',
            'MAIL FROM:<' . $from . '>' . $useVerp,
            250
        );
    }
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.