By default, Instant Search in Outlook returns results only from the currently selected folder and the Instant Search Pane ...

By default, Instant Search in Outlook returns results only from the currently selected folder and the Instant Search Pane displays the folder being searched (for example, "Search Inbox"). Enabling this setting expands the scope for Instant Search to all folders in the current module (for example, Mail or Calendar). The Instant Search Pane displays the module that is being searched (for example, "Search All Mail Items").