Application Settings .NET Core

appsettings.json

  "ApplicationSettings":{
   "DefaultSMTPGuid" : ""
 }

Startup.cs

services.Configure<AppSettings>(Configuration.GetSection("ApplicationSettings"));

AppSettings

   public class AppSettings
   {
       public string DefaultSMTPGuid { get; set; }
   }

MessageService.cs

using Microsoft.Extensions.Options;

private readonly AppSettings _appSettings; 
public MessageService(IOptions<AppSettings> appSettings)
{
   _appSettings = appSettings.Value;
}

_appSettings.DefaultSMTPGuid