However, you can get multiple Outlook windows if you use the shortcut to activate Outlook when it is already running. Replacing that shortcut to Outlook with the following AutoHotkey script will prevent a multiple window side-effect:
#NoEnv ; Recommended for performance and compatibility with future AutoHotkey releases.
SendMode Input ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir% ; Ensures a consistent starting directory.
IfWinExist, ahk_class rctrl_renwnd32
WinActivate
Else Run, C:\Program Files\Microsoft Office\Office12\OUTLOOK.EXE