When you run Windows Live Mail in In Windows 7, you may have noticed that when you right-click on its notification tray icon you no longer get the “Hide window when minimized” option.
And even when minimized, WLMail tab will continue to be present on the taskbar.
Minimize Windows Live Mail to System Tray Notification Area
To get this right-click option back, close Windows Live Mail, right-click on the WLMail shortcut icon > Properties > Compatibility tab > select run this program in compatibility mode for Windows Vista > Apply > OK.
That's it.