protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            try
            {
                string mail = Session["user"].ToString();
                if (mail != null)
                {
                    RegisterStartupScript("test", "<script>window.location='/myaccount.aspx'</script>");
                }
            }
            catch { }
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Session["user"] = txtEmail.Text;
        
        RegisterStartupScript("TestEvent", "<script>window.location='/myaccount.aspx'</script>"); 
    }