bitwarden-server/util/Mail/Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;

namespace Bit.Mail
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services) { }

        public void Configure(IApplicationBuilder app)
        {
            app.UseFileServer();
        }
    }
}