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.
Every week, the folks at InVision send a roundup of their best blog content, their favorite design links from the week, and a new opportunity to win a free t-shirt. (Seriously. They give away a new design every week.) They also sometimes have fun survey questions where they crowdsource for their blog. This week's, for example, asked subscribers what they would do if the internet didn't exist.
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.