NOTE: Similar steps can be followed to bring back minimize to system tray feature in Windows Live Messenger under Windows 7.
When I installed Windows Live Mail in Windows 7, I found that "Hide window when minimized" option was missing in Windows Live Mail system tray context menu.
Its one of the most essential option. It allows you to minimize the Windows Live Mail window to system tray instead of taskbar. But its not shown in Windows 7 because of some compatibility issues.
Here is a step-by-step tutorial to get the "Hide window when minimized" option back in Windows Live Mail:
1. Right-click on the Windows Live Mail shortcut and select Properties. Here the shortcut might be present on Desktop, Programs menu or anywhere else.
2. Go to "Compatibility" tab and enable "Run this program in compatibility mode for:" option.
3. Select "Windows Vista" from the drop-down list and Apply it.
4. That's it. Now start Windows Live Mail and you'll get the option back in its system tray context menu: