I use a custom js script that unchecked the boxes. I've change the on_toggle_quick_composer function of ThreadComposeMessage Class of mail module :

    /*---------------------------------------------------------
     * OpenERP checkboxes décochées par défaut dans le fil de discussion.
     *---------------------------------------------------------*/
openerp.paramJuliana = function(instance){
    var module2 = instance.mail // loading the namespace of the 'sample' module

    module2.ThreadComposeMessage.include({
        on_toggle_quick_composer: function (event) {
            var self = this;
            var $input = $(event.target);
            this.compute_emails_from();
            var email_addresses = _.pluck(this.recipients, 'email_address');

            var suggested_partners = $.Deferred();

            // if clicked: call for suggested recipients
            if (event.type == 'click') {
                this.is_log = $input.hasClass('oe_compose_log');
                suggested_partners = this.parent_thread.ds_thread.call('message_get_suggested_recipients', [[this.context.default_res_id]]).done(function (additional_recipients) {
                    var thread_recipients = additional_recipients[self.context.default_res_id];
                    _.each(thread_recipients, function (recipient) {
                        var parsed_email = module2.ChatterUtils.parse_email(recipient[1]);
                        if (_.indexOf(email_addresses, parsed_email[1]) == -1) {
                            self.recipients.push({
                                'checked': false,
                                'partner_id': recipient[0],
                                'full_name': recipient[1],
                                'name': parsed_email[0],
                                'email_address': parsed_email[1],
                                'reason': recipient[2],
                            })
                        }
                    });
                });
            }
            else {
                suggested_partners.resolve({});
            }

            // when call for suggested partners finished: re-render the widget
            $.when(suggested_partners).pipe(function (additional_recipients) {
                if ((!self.stay_open || (event && event.type == 'click')) && (!self.show_composer || !self.$('textarea:not(.oe_compact)').val().match(/\S+/) && !self.attachment_ids.length)) {
                    self.show_composer = !self.show_composer || self.stay_open;
                    self.reinit();
                }
                if (!self.stay_open && self.show_composer && (!event || event.type != 'blur')) {
                    self.$('textarea:not(.oe_compact):first').focus();
                }
            });

            return suggested_partners;
        },
    });

};

And I set the email @ in font bold and red by changing the template of .oe_recipients label CSS class

This is exactly what I need to do since it is very dangerous and easy to send internal conversations to potential customers in the middle of a negotiation. I need to disable this checkbox and change the default status to uncheked. Can someone please help by pointing me the steps or the path to edit this file? I am new to OpenERP.

You could delete the outgoing mail server. That way the system won't send any mails. And then just use the messaging inside OERP for the users internally.

Take the latest revision, it has a "Log a note" feature instead of the "Send a message" one.

@Fabien Pinckaers

This is a serious issue that we are also facing, Please provide us a better solution for this, as sending a notification to our real customers for each and every internal conversation between our employs(openerp users).