One of the decisions you have to make when you first set-up your autoresponder is to use single or double opt-in. Single opt-in means when a person submits the sign-up form on your web page he doesn’t have to confirm his email address before he is subscribed or receives a free offer.
Double opt in means the customer has to check his email to confirm his subscription. Only after clicking the link in his email does he get added to your email list. Some autoresponder services only allow double opt-in. This is to reduce spam complaints and to satisfy Internet Service Provider (ISP) requirements.
Pros and cons of single and double opt in