Use this Namespace using System.Net.Mail;
MailMessage mail = new MailMessage();
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.From = new MailAddress(from ID);
mail.To.Add(To ID);
mail.Subject = strsub;
mail.Body = strbody;
mail.Priority = MailPriority.High;
mail.IsBodyHtml = true;
SmtpClient smtp = new SmtpClient();
smtp.Port = 25;
smtp.Host = "smtp.gmail.com";
smtp.Credentials = new System.Net.NetworkCredential("Your Mail id", "password");
smtp.EnableSsl = true;
smtp.Send(mail);