Lee Munroe, the founder of htmlemail.io, created a simple responsive email template and open-sourced it on GitHub, which gained traction and led to him sharing his knowledge through blog posts and speaking at conferences. He later developed a pack of high-quality email templates that solved 80% of use cases for startups and developers, which became incredibly successful with over 800 customers within 18 months. The project taught Munroe that most developers don't enjoy dealing with email development issues, such as cross-client support and inlining CSS, and that there's a need for easy-to-use plug-and-play solutions like HTML Email. With the site's success, Munroe plans to continue developing more developer and design tooling for email, aiming to provide tools and content that enable creators to produce high-quality emails quickly with minimal effort.