Probably .net core

https://jakeydocs.readthedocs.io/en/latest/fundamentals/static-files.html#:~:text=The%20ASP.NET%20static%20file,return%20an%20HTTP%20404%20error.

Yep, it's .NET Core related. Had to add it via the StartUp.cs file. Not even Umbraco-related. Learned something new!

var provider = new FileExtensionContentTypeProvider();
provider.Mappings.Add(".kml", "application/vnd.google-earth.kml+xml");
provider.Mappings.Add(".kmz", "application/vnd.google-earth.kmz");

app.UseStaticFiles(new StaticFileOptions
{
    ContentTypeProvider = provider
});

While this works great, it's breaking dynamic image resizing - don't suppose you have discovered a soution for that? Thanks

Hi All, I have the same problem with .run file. I added similar lines to fix that problem but looks like this is breaking the MediaProtect functionality, anyone can download the .run (all protected files) file if they have the link. Any idea how to fix this? Thank you Anton

If anyone encounters a similar problem, I placed the code after

app.UseUmbraco() {...
...
} 

section in the Startup.cs file and it functioning correctly.

Thanks Anton

Thanks for the info. I had a lot of trouble getting this working without breaking the image crops - or rather images were just displaying at random sizes rather than any errors going off.

This code worked for the MIME type but broke the cropper:

app.UseUmbraco()
    .WithMiddleware(u =>
    {
        u.UseBackOffice();
        u.UseWebsite();
    })
    .WithEndpoints(u =>
    {
        u.UseInstallerEndpoints();
        u.UseBackOfficeEndpoints();
        u.UseWebsiteEndpoints();

    });

//for additional mime types - this will bstop cropped images displaying properly!

var provider = new FileExtensionContentTypeProvider();
provider.Mappings.Add(".msg", "application/vnd.ms-outlook");
app.UseStaticFiles(new StaticFileOptions
{
    ContentTypeProvider = provider
});

This code works for the MIME types without breaking the cropper:

app.UseUmbraco()
    .WithMiddleware(u =>
    {
        u.UseBackOffice();
        u.UseWebsite();
    })
    .WithEndpoints(u =>
    {
        u.UseInstallerEndpoints();
        u.UseBackOfficeEndpoints();
        u.UseWebsiteEndpoints();

    });

// Set up custom content types -associating file extension to MIME type
var provider = new FileExtensionContentTypeProvider();
// Add new mappings
provider.Mappings.Add(".msg", "application/vnd.ms-outlook");

app.UseStaticFiles(new StaticFileOptions()
{
    ContentTypeProvider = provider
});

I preffer to not call app.UseStaticFiles and I my opinion Composer is better place to do it

 public class CoreComposer : IComposer
 {
     public void Compose(IUmbracoBuilder builder)
     {

         var contentTypeProvider = new FileExtensionContentTypeProvider();
         if (!contentTypeProvider.Mappings.ContainsKey(".kml"))
         {
             contentTypeProvider.Mappings.Add(".kml", "vnd.google-earth.kml+xml");
         }

         builder.Services.Configure<StaticFileOptions>(options => options.ContentTypeProvider = contentTypeProvider);
     }
 }

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