company name is coming form this method  _notify_prepare_template_context in side  addons/mail/models/res_partner.py which is the company name of login user  company_name = user.company_id.name

    @api.model
    def _notify_prepare_template_context(self, message):
        # compute signature
        signature = ""
        if message.author_id and message.author_id.user_ids and message.author_id.user_ids[0].signature:
            signature = message.author_id.user_ids[0].signature
        elif message.author_id:
            signature = "<p>-- <br/>%s</p>" % message.author_id.name
        # compute Sent by
        if message.author_id and message.author_id.user_ids:
            user = message.author_id.user_ids[0]
        else:
            user = self.env.user
        if user.company_id.website:
            website_url = 'http://%s' % user.company_id.website if not user.company_id.website.lower().startswith(('http:', 'https:')) else user.company_id.website
        else:
            website_url = False
        company_name = user.company_id.name
        model_name = False
        if message.model:
            model_name = self.env['ir.model'].sudo().search([('model', '=', self.env[message.model]._name)]).name_get()[0][1]
        record_name = message.record_name
        tracking = []
        for tracking_value in message.tracking_value_ids:
            tracking.append((tracking_value.field_desc,
                             tracking_value.get_old_display_value()[0],
                             tracking_value.get_new_display_value()[0]))
        return {
            'signature': signature,
            'website_url': website_url,
            'company_name': company_name,
            'model_name': model_name,
            'record_name': record_name,
            'tracking': tracking,
        }