Outlook's Restore Window button doesn't work?

Close Outlook then open the registry editor. Find and delete the values atHKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\Office Explorer where xx is your version of Outlook. Delete Frame , and if you have one for Namespaces, delete it as well. When you restart Outlook, it will open at full screen. Resize the window as desired.

HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\Office Explorer
REG_BINARY: Frame
REG_BINARY: Namespaces