public static void Run() { //ExStart: RetreiveExtAttributesForCalendarItems IEWSClient client = EWSClient.GetEWSClient("https://exchange.office365.com/Exchange.asmx", "username", "password"); //Fetch all calendars from Exchange calendar's folder string[] uriList = client.ListItems(client.MailboxInfo.CalendarUri); //Define the Extended Attribute Property Descriptor for searching purpose //In this case, we have a K1 Long named property for Calendar item PropertyDescriptor propertyDescriptor = new PidNamePropertyDescriptor("K1", PropertyDataType.Integer32, new Guid("00020329-0000-0000-C000-000000000046")); //Fetch calendars that have the custom property IList <MapiCalendar> mapiCalendarList = client.FetchMapiCalendar(uriList, new PropertyDescriptor[] { propertyDescriptor }); foreach (MapiCalendar cal in mapiCalendarList) { foreach (MapiNamedProperty namedProperty in cal.NamedProperties.Values) { Console.WriteLine(namedProperty.NameId + " = " + namedProperty.GetInt32()); } } //ExEnd: RetreiveExtAttributesForCalendarItems }