I have a specific file type of .notebook that IIS is blocking. I tried going into request filtering and adding .notebook with allow set to true, but I still get the 404. Anything else in this folder will download, just this one type is being blocked.
I'm not pushing the download via headers, this is typing in the URL of the file directly.
For reference this is the relevant section that was added to the web.config when I made the change
<security>
<requestFiltering allowDoubleEscaping="false">
<fileExtensions>
<add fileExtension=".notebook" allowed="true" />
</fileExtensions>
</requestFiltering>
</security>