Most people would say that email marketing is cheap, but that implies that it is of little quality and in this case it's quite the opposite. Email marketing is a valuable and high quality technique for reaching people with your company’s message but does not have to cost a lot.
Autoresponders is the name given to a class of software which is designed to automatically respond to any e-mails sent to your address. These programs can be simple or complex depending on the users needs.
Email marketing is obviously the most profitable marketing strategy. All the "big guys" are talking about thousands they make every week, just by blasting an email to their list.
When you are building the list of subscribers and they are getting as an example a "free diet plan" from your site. The niche is not targeted. Yes you know they are people with a weight loss issue!