using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {       

        List<IEmailClient> clients = new List<IEmailClient>();

        clients.Add(new SendGrid());

        clients.Add(new MailJet());

        var emailService = new EmailService(clients);

        emailService.sendEmail();

    }   

}

​

public class EmailService

{

    protected List<IEmailClient> clients;

    public EmailService(List<IEmailClient> clients)

    {

        this.clients = clients;

    }

    public void sendEmail()

    {

        foreach (IEmailClient client in this.clients)

        {

            if (client.send()) {

                break;

            }

        }

    }

}

​

public interface IEmailClient

{

    bool send();

}

​

public class SendGrid: IEmailClient

{

    public bool send()

    {

        var error = true;

​

        Console.WriteLine("SendGrid sending email");

​

        if (error) {

            Console.WriteLine("Error");     

            return false;

        }

        Console.WriteLine("Sendgrid email sent");

        return true;        

    }

}

​

public class MailJet: IEmailClient

{

    public bool send()

    {

        var error = false;

​

        Console.WriteLine("Mailjet sending email");

​

        if (error) {

            Console.WriteLine("Error");     

            return false;

        }

        Console.WriteLine("Mailjet email sent");

        return true;        

    }

}