Recently,[when?] there has been a rapid increase in online lead generation: banner and direct response advertising that works off a CPL pricing model. In a pay-per-acquisition (PPA) pricing model, advertisers pay only for qualified leads resulting from those actions, irrespective of the clicks or impressions that went into generating the lead. PPA advertising is playing an active role in online lead generation.
The most advanced email marketing services offer custom workflows where you can specify triggers based on actions (such as opening an email or making a purchase) or on inaction (such as ignoring emails). With these services, you can also set up a series of emails (such as tutorials) to be sent to segments of users, and you can pause or stop a campaign at any time. You can also move contacts into new segments once they have completed tutorials.