This opens the Outlook search ribbon and places an active cursor in the search bar from anywhere within Outlook. The Ctrl+E or F3 shortcut is what you’re looking for. The reflex action to find anything these days is to use the Ctrl+F shortcut, but this actually forwards the email that’s currently selected. These shortcuts will help you navigate your inbox faster and effectively.
If you receive a lot of emails, it’s likely you frequently use the search function. There are many shortcuts to learn in Outlook, and some come in handy more than others.