Outlook Search Folders are virtual collections that display messages matching selected criteria. They do not move or duplicate the original items, allowing a user to review unread, flagged, large, or otherwise relevant mail across its existing mailbox folders.

Find Related Outlook Items Without Moving the Originals

A search folder can also help locate messages with attachments or particular keywords. Microsoft distinguishes predefined criteria in new Outlook from advanced custom search folders in classic Outlook, and notes that results cannot span multiple PST data files. Choose the criteria around what you need to retrieve rather than creating another physical filing location.