Explorer.SelectAllItems Method (Outlook)
Selects all items that are contained in the current view of the active explorer.
If one or more groups are collapsed in the current view, calling SelectAllItems does not select items in the collapsed groups. Only items in expanded groups are selected.
If the current view is a calendar view, calling SelectAllItems selects all appointments and all-day events in the view. Calling SelectAllItems on a calendar view does not select items in the Daily Task List.
The SelectionChange event fires only once after the SelectAllItems method is called.
If the current view or current folder does not contain any items, calling SelectAllItems does not result in any change to the selection and does not fire the SelectionChange event.
SelectAllItems raises an error if the item is being edited in the current view, or the current view is a conversation view.