using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Mail; // HERE!
using System.Text;
using System.Threading.Tasks;

namespace MyMail
{
    class Program
    {
        static void Main(string[] args)
        {
            SmtpClient client = new SmtpClient();
            client.Port = 587;
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.UseDefaultCredentials = false;
            client.Credentials = new System.Net.NetworkCredential("yaroslaw@live.ru", "pass");
            client.Host = "smtp.live.com";
            client.EnableSsl = true;

            MailMessage mail = new MailMessage("yaroslaw@live.ru", "knitershift@gmail.com");
            mail.Subject = "this is a test email.";
            mail.Body = "this is my test email body";

            client.Send(mail);

            //var mail = new MailMessage();
            //mail.From = new MailAddress("youremail@hotmail.com");
            //mail.To.Add("to@gmail.com");
            //mail.Subject = "Test Mail - 1";
            //mail.IsBodyHtml = true;
        }
    }
}