The majority of earnings on the health and wellness website 7Sigma Physiques come from email funnels, with ConvertKit being the email service provider used to make it happen. The author shares tips for boosting sales and engagement using ConvertKit, including adding a countdown timer to create FOMO, setting up custom unsubscribe links to cater to different subscriber interests, A/B testing subject lines to improve open rates, resenting emails to unopens, and cleaning up the email list by removing cold subscribers to reduce cost, improve deliverability, and see more accurate data. These tips are intended to help users optimize their ConvertKit campaigns for better results.