Something.cs

  public void Validar(Object sender, EventArgs e)
        {
            var email = EntryEmail.Text;
            var emailPattern = "^([\\w\\.\\-]+)@([\\w\\-]+)((\\.(\\w){2,3})+)$";

            if (!String.IsNullOrWhiteSpace(email) && !(Regex.IsMatch(email, emailPattern)))
            {
                LabelError.Text = "EmailVerification Failed";
            }
            else
            {
                LabelError.Text = "";
            }
        }