Double opt-in is optional at Mailchimp. Customers can add emails directly and check a box saying "yes this customer gave me permission". Aweber uses double op

Double opt-in is optional at Mailchimp. Customers can add emails directly and check a box saying "yes this customer gave me permission". Aweber uses double opt-in and there is no way around it. But that is a double edged sword when you've got a business to run.