enviar_email.cs

// Colocar no using 
// using System.Net.Mail;

SmtpClient SmtpServer = new SmtpClient("smtp.live.com");
var mail = new MailMessage();
mail.From = new MailAddress("email_remetente@hotmail.com");
mail.To.Add("email_destino@gmail.com");
mail.Subject = "Test Mail - 1";
mail.IsBodyHtml = true;
string htmlBody;
htmlBody = "Write some HTML code here";
mail.Body = htmlBody;
SmtpServer.Port = 587;
SmtpServer.UseDefaultCredentials = false;
SmtpServer.Credentials = new System.Net.NetworkCredential("email_remetente@hotmail.com", "senha");
SmtpServer.EnableSsl = true;
SmtpServer.Send(mail);