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namespace Core.Interfaces
{
    public interface SendMail
    {
        void sendMail(string recipient, string subject, string message);
    }
}

zs40x

using Core.Interfaces;
using Core.Model;

namespace Core.Services
{
    public class NotificationService
    {
        SendMail sendMail;

        public NotificationService(SendMail _sendMail)

zs40x

using UserEMailNotificationSender.Infrastucture;
using UserEMailNotificationSender.Model;

namespace UserEMailNotificationSender.BL
{
    class SMTPNotificationSender
    {
        SMTPClient smtpClient = new SMTPClient();

        public void sendNotificationForUser(User userToNotify)

zs40x

using UserEMailNotificationSender.BL;
using UserEMailNotificationSender.Model;

namespace UserEMailNotificationSender
{
    class Program
    {
        static void Main(string[] args)
        {
            User aUser = new User("TheUser", "the_user@mail_service.com", false);