How to Send CC email on send by email in sale Quotation, Should I use different keyword for email cc?

Question

I am Overloading the get_mail_values method of mail.compose.message. I have added email_cc field only and I am expecting the mail should go to both recipients.

@api.multi
    def get_mail_values(self, res_ids):
        """Generate the values that will be used by send_mail to create mail_messages
        or mail_mails. """
        self.ensure_one()
        results = dict.fromkeys(res_ids, False)
        rendered_values = {}
        mass_mail_mode = self.composition_mode == 'mass_mail'

        # render all template-based value at once
        if mass_mail_mode and self.model:
            rendered_values = self.render_message(res_ids)
        # compute alias-based reply-to in batch
        reply_to_value = dict.fromkeys(res_ids, None)
        if mass_mail_mode and not self.no_auto_thread:
            # reply_to_value = self.env['mail.thread'].with_context(thread_model=self.model).browse(res_ids).message_get_reply_to(default=self.email_from)
            reply_to_value = self.env['mail.thread'].with_context(thread_model=self.model).message_get_reply_to(res_ids, default=self.email_from)

        for res_id in res_ids:
            # static wizard (mail.message) values
            mail_values = {
                'subject': self.subject,
                'body': self.body or '',
                'parent_id': self.parent_id and self.parent_id.id,
                'partner_ids': [partner.id for partner in self.partner_ids],
                **'email_cc' : self.partner_ids_cc,**
                'attachment_ids': [attach.id for attach in self.attachment_ids],
                'author_id': self.author_id.id,
                'email_from': self.email_from,
                'record_name': self.record_name,
                'no_auto_thread': self.no_auto_thread,
                'mail_server_id': self.mail_server_id.id,
            }
            # mass mailing: rendering override wizard static values
            if mass_mail_mode and self.model:
                # keep a copy unless specifically requested, reset record name (avoid browsing records)
                mail_values.update(notification=not self.auto_delete_message, model=self.model, res_id=res_id, record_name=False)
                # auto deletion of mail_mail
                if self.auto_delete or self.template_id.auto_delete:
                    mail_values['auto_delete'] = True
                # rendered values using template
                email_dict = rendered_values[res_id]
                mail_values['partner_ids'] += email_dict.pop('partner_ids', [])
                mail_values.update(email_dict)
                if not self.no_auto_thread:
                    mail_values.pop('reply_to')
                    if reply_to_value.get(res_id):
                        mail_values['reply_to'] = reply_to_value[res_id]
                if self.no_auto_thread and not mail_values.get('reply_to'):
                    mail_values['reply_to'] = mail_values['email_from']
                # mail_mail values: body -> body_html, partner_ids -> recipient_ids
                mail_values['body_html'] = mail_values.get('body', '')
                mail_values['recipient_ids'] = [(4, id) for id in mail_values.pop('partner_ids', [])]

                # process attachments: should not be encoded before being processed by message_post / mail_mail create
                mail_values['attachments'] = [(name, base64.b64decode(enc_cont)) for name, enc_cont in email_dict.pop('attachments', list())]
                attachment_ids = []
                for attach_id in mail_values.pop('attachment_ids'):
                    new_attach_id = self.env['ir.attachment'].browse(attach_id).copy({'res_model': self._name, 'res_id': self.id})
                    attachment_ids.append(new_attach_id.id)
                mail_values['attachment_ids'] = self.env['mail.thread']._message_preprocess_attachments(
                    mail_values.pop('attachments', []),
                    attachment_ids, 'mail.message', 0)

            results[res_id] = mail_values
        return results

As per my conclusion mail.compose.message passing control to mail.mail object and send method of mail.mail object is responsible to send mail to normal recipients and CC recipient.

Please suggest me where i am doing mistakes?