An opt-in box, lead capture box, or sign up box is an element on your website with the purpose of capturing leads and growing an email marketing list.
The premise behind a website opt-in box is to capture the names and emails of visitors who want to learn more from you, stay in touch with you, and hear from you in the future — those who aren’t quite ready to hire you or buy from you — so you can market to them by email in the future.
When opt-ins first became popular, simply offering an email newsletter subscription worked great for conversions. At that time having an email newsletter made you cool because not many people had one! But as consumers became more internet savvy, and spam became more prevalent, consumers became more protective of their email addresses and website owners were forced to up the ante.