Core_Email::send

public function send()
{
    if ($this->_replyto_flag === false)
    {
        $this->reply_to($this->_headers['From']);
    }

    if ( ! isset($this->_recipients) && ! isset($this->_headers['To'])
        && ! isset($this->_bcc_array) && ! isset($this->_headers['Bcc'])
        && ! isset($this->_headers['Cc']))
    {
        $this->_set_error_message('lang:email_no_recipients');
        return false;
    }

    $this->_build_headers();

    if ($this->bcc_batch_mode && count($this->_bcc_array) > $this->bcc_batch_size)
    {
        return $this->batch_bcc_send();
    }

    $this->_build_message();
    return $this->_spool_email();
}