Change your inputs for AspNet textboxes. Change your input button for an AspNet button. Add a handler for the OnClick event. There, explicitly add the email from the textbox to the session object. The following code is not tested, so check it before using
protected void MyButton_Click(object sender, EventArgs e){
Session.Add(txtEmail.Text);
Response.Redirect("~/MyOtherPage.aspx");
}