Studies show that customers who buy a product are likely to buy another one in the future. Since it is far easier to make a sale to a proven mailing list customer than it is to attract a new one, it makes sense to compile a mailing list of customers. That way, should you decide to promote a new product in the future, you can e-mail a sales pitch to your list and know that the message will likely be read by customers who are "ready to buy."
The best part of having a mailing list is that you can automate a lot of the process by using an autoresponder. An autoresponder is an online service that handles mailings and mail lists for you, usually for a small monthly fee. Two of mailing list the more popular services are Aweber and Get Response. These services allow you to create a simple form that appears on your Website, asking visitors for their name and e-mail address.
You can usually entice them to sign up by offering a free report of some sort in exchange for the information. Once they fill in the form and click the submit button, they are automatically sent a confirmation e-mail, followed by mailing list a link to download the report you offered them. From that point on, unless they unsubscribe, they are members of your mailing list.