Where do I find my Shopping Car emails?

[yoder]

Hello,
When I go to the "database table manager" I only find about half of my shopping cart customers in the "car_customers" data table. I this because the customers did not want the shopping cart to "remember the shipping and billing information?

I would like to capture shoppers email addresses for marketing purposes. Is there an option on the shopping cart that I can have them select a radio button asking "would you like to get email notifications on specails", which could build this shopping cart data table?

Thanks.