In 2015 I devoured Tim Ferriss’ 4-Hour Workweek and fell so deeply in love with the idea of passive income that I created an online store for men’s fashion. The task at hand—yours, too, if you’re reading this guide—became: how to sell? I blogged, ran giveaways and collected 27,000 Instagram followers in the first year. But it was email marketing that became my star salesperson. The experts told me that this familiar tool was the most effective sales channel after word of mouth, and it’s as true today as it was then—even in a world where social media is everyone’s darling.