email newsletter automatically

Have a look here creating window service
http://www.csharpcorner.com/UploadFile/mahesh/window_service11262005045007AM/window_service.aspx

Following is sample code how to send periodically.
public partial class Service1 : ServiceBase
    {
        public Service1()
        {
            InitializeComponent();
        }
        System.Timers.Timer testTimer = new System.Timers.Timer();

        protected override void OnStart(string[] args)
        {
            testTimer.Enabled = true;
            testTimer.Interval = 1000;
            testTimer.Elapsed += new System.Timers.ElapsedEventHandler(testTimer_Elapsed);
        }
        private void testTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            /* you can check in the data base which mail should send & send email  */
        }

        protected override void OnStop()
        {
            testTimer.Enabled = false;
        }
    }