As your online business becomes more successful you are able to provide great products and service to your customers. When mailing list a customer receives great service there is every chance they will return to see what else you have to offer. They could even recommend your product or service to others, thus generating even more business for you.
The more traffic that comes to your site means there is a good chance you can get them to subscribe to your mailing list. A mailing list or opt-in list is essentially an autoresponder that allows you to capture the name and email address of mailing list a customer. From there your autoresponder can be set to automatically send out promotional material or news to your customer via email.
By using email you are cutting costs. Email is free and allows you to send out articles, advertisements etc. Having an opt-in means mailing list customers have agreed to sign up and receive further mailings from you. They are unlikely to delete your mail or mark it as spam. The result is your subscribers are continually reminded about your products and services. There is every chance they will purchase or recommend to others.