Thus, many firms rely not on spam but on opt-in e-mail promotions. One of the primary ways of having customers volunteer their e-mail addresses is through mandatory registration on a Web site. Firms that rely on registrations can cull their customers' e-mail address and send direct promotional materials to them. Targeted to the customer's interests, the e-mail flyers and brochures have the potential to bring in consumer traffic to Web sites or in some cases to brick-and-mortar stores. The disadvantage with using e-mail as a means of direct promotion is that many consumers do not provide a valid e-mail address or reserve a spare, hardly used e-mail address specifically for Web site registrations. Viral marketing has become a potentially robust form of Web-based promotion. Including cleverly placed press releases, articles, and blog entries, viral marketing...

Word-of-mouth marketing empowers the consumer, honors the consumer's intelligence and ability to choose, and bypasses more annoying types of online advertising such as pop-ups and spam. Moreover, the word-of-mouth advertising can take on a life of its own and spread far and wide at virtually no cost to the firm. In fact, the consumer does much of the promotion inadvertently.
The main drawback with viral marketing is that many consumers might bypass the promotional material altogether. Those who have little time to browse blogs or read online articles will miss out on the promotional material. Still, viral marketing does allow for more social presence, because many of the consumers participating in the spread of information are perceived as "real people" and not as an impersonal firm.