Email authentication

I need to have some sort of email authentication on some sites I have built in ASP and VBScript. I have users sign up for a 7 day trail of some news sites and then when their trail has ended, lock them out of the site unless they subscribe. Now this all works fine, but some people have been entering false email addresses and managing to slip through the net.

Now, once they have entered an email address, I need to send an email to that address and supply a link to verify that email address thus activating that trial account.

I can't figure out the sending of the email with a verification link in it and how it applies to the correct record once the link in the email has been clicked.

I think this is quite standard nowadays, but I can't seem to find anything on the web for ASP email verification other than the usual check for the '@' and '.' in an email address...

Has anybody got any tutorials/samples on how I might achieve this, or even recommend an extension or similar.

Thanks.

Mat