This is a process described by Seth Godin known as permission marketing. The core concept of this idea is that you never market to someone that doesn’t want it, you first have to ask them for their permission. When someone signs up to your email not only do they become a warm lead but they give you their permission to send them offers and to market to them.
Push marketing is a proactive technique that enables e-marketers to "push" their product/service information to Web visitors or shoppers without their requesting it. Banner advertising, pop-up advertising, e-mail promotion, and spamming belong to push marketing. For instance, e-marketers can rent designated space from Internet service providers such as America Online or MSN for their banner or pop-up ads. Using animated graphics, appealing messages, and links, e-marketers try to lure visitors to their sites to buy their products or services. Many Internet users, however, find such ads annoying and employ software that blocks pop-ups and banner ads. <