List Building is one of the most important aspects of internet marketing. If you are not familiar with list building, you should learn about it. Opt in email campaigns are simply one of many traffic sources, just like Search Engine Marketing (SEM), Social Media Marketing (SMM) and Pay Per Click (PPC) are sources of traffic. That being said, not all sources are equal. Whereas social media marketing brings relatively low quality traffic, search engine marketing and pay per click marketing bring high quality traffic. On that same note, list building can also bring high quality traffic over and over again. But it can only do this if your list receives and opens your email. Many internet marketers accomplish this by providing consistent value through a newsletter.