An opt-in box allows people to provide their name and email to sign up for your email marketing campaign. It is important to include an opt-in box on websites, blog posts, videos, and other online content to build an email list. Squeeze pages, which only contain an opt-in box, often have higher signup rates than websites since they have fewer distractions. Building an email list is valuable for developing trust with subscribers and marketing to them through email communications over time.