I still get a lot of search hits from people looking for a way to change the extensions that cannot be viewed in Outlook, because Microsoft decided in all her wisdom to mark a lot of extensions as “unsafe”. In Outlook Express there is a nice dialog to change this behaviour, in Outlook there is not. You can do it by editing the registry by hand, but a lot of people are afraid to do so.
For that reason, I created ouau.exe, or “Outlook Unsafe Attachments Unblocker”. It detects your Office version (which you can override) and lists the extension so you can block/unblock them. There’s a handy “select all” radiobutton that will save you some clicking.
Here is a screenshot.
Click here to download the program. It’s in WinRAR format, so you need to extract it first.