You have to click the shortcut for the applicationa and from the properties tab, select to run in comptability mode for Windows Vista SP2, this will allow you to find the item "Hide window when minimized" which is missing for Windows 7.
Thanks to the following detailed article:
http://www.howtogeek.com/howto/19438/minimize-windows-live-mail-to-the-system-tray-in-windows-7/
Thanks to the following detailed article:
http://www.howtogeek.com/howto/19438/minimize-windows-live-mail-to-the-system-tray-in-windows-7/