// 修改的代码
$ctx = stream_context_create(array(
    'ssl' => array(
        'verify_peer_name' => FALSE,
    )
));
$this->_smtp_connect = stream_socket_client(
    $ssl . $this->smtp_host . ':' . $this->smtp_port, 
    $errno,
    $errstr, 
    $this->smtp_timeout,
    STREAM_CLIENT_CONNECT,
    $ctx
);

// 注释原来的代码
// $this->_smtp_connect = @fsockopen($ssl.$this->smtp_host,
//                     $this->smtp_port,
//                     $errno,
//                     $errstr,
//                     $this->smtp_timeout);