The drop-down menu next to the search box offers some predefined filters to quickly reduceg the messages listed to their status or priority.
The filter rules selected here are applied in addition to the search term entered in the search box. For example you can choose to only list unanswered messages from Paul by selecting the filter Unanswered and enter “from:Paul” in the search box.
The message filters also depend on the “Scope” selected in the search options menu. Change the scope if you want to expand the active filter to list matching messages from all folders.