From Side Project to $12 Billion: Lessons from Mailchimp’s Founder

Ben Chestnut didn’t plan to build a $12 billion company. He ran a small web-design agency and built an email tool on the side to help clients. That side project became Mailchimp.

Listening to his How I Built This interview with Guy Raz, a few lessons stood out:

1. Start with what you have. Mailchimp grew organically by solving a real customer problem, not by chasing funding.

2. Differentiate through identity. The playful branding wasn’t cosmetic—it made the product approachable in a crowded market.

3. Follow the data. A simple performance spreadsheet revealed where the real business opportunity was.

4. Scale culture intentionally. Growth forced new leadership structures and values alignment.

5. Independence is strategic. Staying private let Mailchimp grow on its own terms and prioritize customers over investors.

   
   

Takeaway: not every billion-dollar idea starts with ambition; many start with curiosity and consistent execution. The key is recognizing traction early and doubling down with focus.