public abstract class Message
    {
     public IMessageSender MessageSender { get; set; }
     public string Subject { get; set; }
     public string Body { get; set; }
     public abstract void Send();
    }


    public class SystemMessage : Message
    {
     public override void Send()
     {
     MessageSender.SendMessage(Subject, Body);
     }
    }


    public class UserMessage : Message
    {
     public string UserComments { get; set; }

     public override void Send()
     {
     string fullBody = string.Format("{0}\nUser Comments: {1}", Body, UserComments);
     MessageSender.SendMessage(Subject, fullBody);
     }
    }


    public interface IMessageSender
    {
     void SendMessage(string subject, string body);
    }


    public class EmailSender : IMessageSender
    {
     public void SendMessage(string subject, string body)
     {
     Console.WriteLine("Email\n{0}\n{1}\n", subject, body);
     }
    }


    public class MSMQSender : IMessageSender
    {
     public void SendMessage(string subject, string body)
     {
     Console.WriteLine("MSMQ\n{0}\n{1}\n", subject, body);
     }
    }


    public class WebServiceSender : IMessageSender
    {
     public void SendMessage(string subject, string body)
     {
     Console.WriteLine("Web Service\n{0}\n{1}\n", subject, body);
     }
    }

    class Program
    {
     static void Main(string[] args)
     {
     IMessageSender email = new EmailSender();
     IMessageSender queue = new MSMQSender();
     IMessageSender web = new WebServiceSender();

     Message message = new SystemMessage();
     message.Subject = "Test Message";
     message.Body = "Hi, This is a Test Message";

     message.MessageSender = email;
     message.Send();

     message.MessageSender = queue;
     message.Send();

     message.MessageSender = web;
     message.Send();

     UserMessage usermsg = new UserMessage();
     usermsg.Subject = "Test Message";
     usermsg.Body = "Hi, This is a Test Message";
     usermsg.UserComments = "I hope you are well";

     usermsg.MessageSender = email;
     usermsg.Send();

     Console.ReadKey();
     }
    }