Search All Mac Outlook 2016 Messages
Under the Edit menu select the "Find" sub-menu and select "Advanced Find..." or press Command-Shift-F
A search toolbar will appear.
Click the "All Mail" icon to search all mail within Outlook.
Below the toolbar enter your search items in the "Items Contains" search box.
Add additional search criteria by pressing the + button at the end of the search box.
When done click "Close Search" on the toolbar.