The opt-in list generation method allows leads to be generated and customers can be targeted specifically through their interests. The most common opt-in method in use today is through Web sites and emails, whereby after visiting a Web site, users can choose to receive information either directly related to that product or from third parties with similar products.

This is also known as permission-based marketing, and is an incredibly useful way to target potential customers more specifically. However, the technique is not limited to internet marketing. After making an order for a product by mail, there will often be an option to check a box that allows the customer's information to be used for marketing purposes.

A further method of ensuring that the person is interested in a particular product or service is by using the double opt-in method. This is very common with email newsletters, whereby an email is sent to the user's email address, and the user must then click on a link to confirm that they want to be on the list. This is a protective method to prevent people receiving too much spam mail, but it is also a good marketing tool as it means the people on the list are genuinely interested in receiving it.