On the Internet, Web sites and search engines can be excellent sources of leads, although the process can be time consuming. Web sites, such as TechTarget.com, have evolved for the specific purpose of making it easy for personnel to obtain leads. Companies have emerged that specialize in lead generation for a fee. They perform the research, and then provide the client with a list of leads. Services of this kind have been used by insurance companies, real estate agents, wholesalers, marketing firms, private investigators, research scientists and educational institutions.
The first autoresponders were created within mail transfer agents that found they could not deliver an e-mail to a given address. These create bounce messages such as "your e-mail could not be delivered because..." type responses. Today's autoresponders need to be careful to not generate e-mail backscatter, which can result in the autoresponses being considered E-mail spam.
Over time, the popularity of email marketing campaigns resulted in personal email inboxes that were overflowing with the latest and greatest offers. Email campaigns grew and people grew tired of them. Laws that allowed customers to unsubscribe breathed new life into email marketing campaigns as customers could easily pick and choose the companies they were interested in.