using System;

using System.Linq;

using System.Threading;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<string> addresses = GetEmailAddresses();

        var skipCount = 0;

        const int takeCount = 1;

        TimeSpan period = TimeSpan.FromSeconds(1);

​

        var timer = new System.Threading.Timer(e =>

        {

            foreach (string address in addresses.Skip(skipCount).Take(takeCount))

            {

                SendEmailAddress(address);

            }

            Interlocked.Add(ref skipCount, takeCount);

        }, null, TimeSpan.Zero, period);

​

        while (addresses.Count > Interlocked.CompareExchange(ref skipCount, int.MinValue, int.MinValue)) {

            Thread.Sleep(1000);

        }

​

        timer.Dispose();

        Console.WriteLine("Fine");

    }

    private static List<string> GetEmailAddresses()

    {

        return new List<string> { "a", "b", "c" };

    }

    private static void SendEmailAddress(string email)

    {

    }

}