Mail makes extensive use of contextual menus: Control-click on a message, the toolbar, or an item in the Mailbox Sidebar to open a pop-up menu that offers various commands, as shown below. If you have a two-button mouse, right-click on an item to show a contextual menu.
Using contextual menus is just a convenient way to access menu commandsthere is nothing in a contextual menu that you can't find in the main menu bar across the top of your screen.
Hold down the Control key (not the Command key) and click on any message in the Viewer window to open a contextual menu.