readonly Outlook.Application _outlookApp = new Outlook.Application();

        private void ThisAddIn_Startup(object sender, System.EventArgs e)
        {
            _outlookApp.ItemLoad += new Outlook.ApplicationEvents_11_ItemLoadEventHandler(test_ItemLoad);
        }

        void test_ItemLoad(object item)
        {
            if (item is Outlook.AppointmentItem)
            {
                var appt = item as Outlook.AppointmentItem;
                appt.PropertyChange += new ItemEvents_10_PropertyChangeEventHandler(appt_PropertyChange);
            }
        }

        void appt_PropertyChange(string name)
        {
            MessageBox.Show(string.Format("Name: {0}", name));
            xxx
        }

readonly Outlook.Application _outlookApp = new Outlook.Application();

        private void ThisAddIn_Startup(object sender, System.EventArgs e)
        {
            _outlookApp.ItemSend += new ApplicationEvents_11_ItemSendEventHandler(OutlookAppItemSend);
        }

        void OutlookAppItemSend(object item, ref bool cancel)
        {
            if (item is Outlook.AppointmentItem)
            {
                var appt = item as Outlook.AppointmentItem;
                foreach (Outlook.Recipient recipient in appt.Recipients)
                {
                    MessageBox.Show(string.Format("Rctp {0} ", recipient.Name));
                }

            }
....