Double opt-in is a system designed to help protect email subscribers from unwanted email communications. When a business uses double opt-in, they first ask the subscriber for their permission to send emails. Once the subscriber has confirmed their email address, the business then sends a second email asking the subscriber to confirm their subscription. Only after the subscriber has confirmed their subscription a second time will they begin receiving email communications from the business. This system helps to ensure that only those who have explicitly expressed an interest in receiving email communications from a business will receive them. As a result, it helps to reduce spam and protect email subscribers from unwanted email communications.