Marketing is a blend of science and art and it should be approached very carefully and strategically. One of the most frequent methods of marketing and awareness building are mailing lists to which people sign up in order to receive promotions, discounts, free products or services and so on.
However, when it comes to populating and building your e-mail lists it is extremely important to allow people to choose whether they want to subscribe on their own. No matter what, DO NOT add people to your lists WITHOUT their knowledge and explicit permission to do so. Build integrity with your community where your actions and words match each other and are consistent across the board. People need to be able to trust you before they invest any additional time or resources. Respect their time, privacy and always be professional.