using (MailMessage mm = new MailMessage("admin@mydomain.com ", "user@hotmail.com"))
    {
        mm.Subject = "Activation Account";
        string body = "Welcome ";
        mm.Body = body;
        mm.IsBodyHtml = true;
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "relay-hosting.secureserver.net";
        NetworkCredential NetworkCred = new NetworkCredential("admin@mydomain.com", ConfigurationManager.AppSettings["emailPassword"]);
        smtp.UseDefaultCredentials = false;
        smtp.Credentials = NetworkCred;
        smtp.Port = 25;
        smtp.Send(mm);
    }