Program.cs

using System.IO;
using Microsoft.Extensions.Configuration;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

namespace ResidentMail
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureAppConfiguration((hostContext, config) =>
                {
                    config.SetBasePath(Directory.GetCurrentDirectory());
                    config.AddJsonFile("mailsettings.json", optional: true, reloadOnChange: true);
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}