Hmm, try this (not sure if you will be satisfied):
- I don't know how to change an exe directly (and usually don't change them

)
- Right click on shortcut of outlook, or just create one (send to->desktop)
- Shortcut tab->Change Icon
- It will show some default icons
- select one and click apply
- start program with that shortcut
if you don't like the default icons
- select browse and open an icon file
You should be able to download from internet
or try:
Windows\system32\imageres.dll
Windows\system32\shell32.dll
Windows\system32\DDORes.dll
Windows\System32\moricons.dll (MS DOS Icons)
Please note that this works with regular exe files, but I don't know if it will work with Outlook