The Quick Filter Bar is shown below.

Opening
–Main Menu > View > Toolbars > Quick Filter Bar.
–Message List > Quick Filter.
–Hotkeys: Ctrl+Shift+K or Shift+Cmd+K.
Elements
–
button: apply filters when switching folders.
–
field: enter the text of the search query.
–
button: view only unread messages.
–
button: view only messages marked with a star.
–
button: view only messages from people in your address book.
–
button: view only tagged messages.
–
button: view only messages with attachments.