There's Money In The List
Affiliate marketers and other online marketers have long seen the advantage of email lists. Either through the ethical purchase of a genuine opt-in list, or by building your own list from your website, it's possible to generate a large number of email addresses belonging to relevant individuals. Lists are considered among the most beneficial forms of online marketing because they can be approached time and time again (when done properly, of course).
Opt in email lists give the email marketer a head start. It's not necessary to look for potential customers on other websites because the list contains those leads. The big challenge in email marketing is creating a powerful email that converts and gets past spam email filters. Presuming you can achieve this, though, it's possible to profit from affiliate schemes, paid advertising, and direct sales.
Every email on your list should have opted in to receive communication from you regardless of whether you collected the data manually or purchased the list. Care should always be taken when purchasing lists to ensure that this really is the case. Sending unsolicited email will inevitably mean that your will be labelled a spammer and not only will future email marketing campaigns fail because of this but you may struggle in many other areas of running your business as well.
Well targeted email campaigns can generate a lot of business for comparatively little time, effort, and investment. Remove anybody that requests to opt out of future emails and you can use the list time and time again to announce new products, extra incentives to purchase, and much more.