How To Block Email Addresses

I want to block certain email addresses like,(See the MailTo Section, I don't want the Sandra email address), through my online forms. I've been receiving spam from people using the forms. My code below is ASP. The code basically sends the form data to 3 email addresses and send the visitor who filled out the form an HTML style email message as confirmation. I added an IF THEN statement (Look at the MAIL TO) for the unwanted email address thinking it would do the trick but it doesn't block or send the email to the unwanted email address. Here's the beginning of my code. Any help would be greatly appreciated. NOTE: I replaced the wanted email addresses with phony names because they are private.

<%
If request.form("Email")="" then
response.write "<p><br><center><font face='arial' size=3>"
response.write "<b>Please don't forget to enter your"
response.write " Email address!</b></font>"
response.write "<form>"
response.write "<input type=""button"" value=""Return to Form"""
response.write " onclick=history.go(-1)></form>"

Else ........