When the search results are displayed, a Search ribbon will appear, allowing you to further refine your results. If you do not select any of these specifics, Outlook will search all the basic headers, the subject, and the body of the message. While typing in the search box, you'll be offered the option of specifying where in the message to search (from, to, subject, etc.). It does NOT include sub-folders of that folder (but see the bullets below). This method searches only the folder you've selected. You can search for a particular message by clicking on the folder where the message is stored, then using the search bar in the upper-right corner of the Outlook window. Quick Search (one mail folder, but can be modified) Advanced Find (multiple folders, more options).Here are two methods that many find useful. Outlook 2016 for Mac provides searching at various levels of complexity.
