Blocking Access To A Page

I have a form on an .html page that I have a visitor submit the results from which redirects to an ASP script. The problem is the visitors are viewing the source of the page and going directly to the .asp file instead of filling out the form.

I'm trying to use the following script so the page can only be accessed if the user is sent from the form. If they try to access it directly, it will send them back to the page with the form. Here is what I'm using, but it keeps blocking access to the page wheter the form is filled out, or access directly:

If Request.Form("email") <> "Yes" Then
Response.Redirect "http://www.domain.com/form.asp"
End If