$config = array(
    'mailtype' => 'html',
    'bcc_batch_mode' => true,
    'bcc_batch_size' => 200
);
$this->load->library('email');
$this->email->clear(TRUE);
$this->email->initialize($config);
$this->email->from('xxxx@site.yyy', 'Site name');
$this->email->to('');
$this->email->bcc($emails); // array()
$this->email->subject($subject); // string
$this->email->message($content); // html content
if( !$this->email->send() ) {
    die('Error!');
}