You were browsing online one day. You had this thing on your mind and you were searching for additional information about it. You came upon this particular site that was quite interesting. You signed up to this site so that can have full access on its pages. A few seconds after you have signed up, you received a message on your e-mail inbox. Ding, ding, ding.. Ever wonder how anyone could compose a message that fast? Wonder no more. The one who composed that message isn't a person. It's a web-based autoresponder program.