For very good reasons, not all extensions are recognized by IIS by default and may return a 404 error when trying to access them from your site. If you have need to add more extensions to be “allowed” – for example if you have embedded font files – you have a few different options.
One method is to add the new mapping in the MIME Mappings module of the IIS7 Manager which you can run and use locally, or you can use the IIS7 Manager for Remote Administration to connect to your site remotely and manage this feature. Once connected, the link below shows where to find this module and make the required change.
That same link gives a little bit of information about managing the mime mappings via your site config file, but not a lot of detail. The link below gives additional information and even a sample web.config file that someone specifically used to manage their mappings.
Some web hosts also have control panels that allow you to manage the mime mappings for your web site. If so, it should be fine to use that too. Any of these three methods should accomplish the same thing.
Once you decide where to manage the mapping, you need to make sure you set it up properly. Different file types have different requirements so you may need to do a little research on your own to determine the exact mapping text. Here’s one sample showing how to map embedded .woff font files: http://www.dirigodev.com/blog/404-errors-in-IIS7-for-embedded-woff-font-files/
I hope this saves you a little time and frustration. Happy hosting!