In the olden days, it was a "mailing list", but mailing list now with the a mature internet, e-mails, instant messaging, and so on, it seems adequate to just use the term "list". If you are looking for customers online, you should have a capture form on each of your web pages to try to obtain new subscribers. What will you do with these names?
Well, for starters, it is highly beneficial to have an autoresponder working for you to e-mail your list automatically. Of course, you mailing list will need to manage the content of the autoresponder series yourself, or have some one set it up for you. The rationale for sending a series of e-mails to your prospects is that most prospects need to see an offer more than once before they commit to a buying decision.
Your autoresponder takes care of that obstacle. Sometimes new prospects can be reluctant to send you their name and e-mail (or other personal details) simply out of fear or suspicion. To get around any reluctance, many online mailing list business types will offer a free item such as an e-book or special report, in exchange for their contact information.