automatic emails in asp.net 2.0 without human interaction.

 can any one advise good logic and model where I can use Recurrsive payment for Customers. Our Customer use our asp.net 2.0 web page and go to google button to complete payment. but for subscription based, how can i send customer automatic emails from asp.net 2.0 to notify them about expiration of their account, so they can go and make a payment to Google. As Google checkout does not support Reccursive payment. Paypal is not an option as this time.
 so in short, How can i send automatic emails in asp.net 2.0 without human interaction.

Thanks, 
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