MailChimp: The abandoned side project that quietly turned into a $700m/year revenue business

tl;dr: a web design agency built the software that would later become MailChimp because they were tired of building email lists from the ground up for each new client.

Reminds me of this advice for aspiring founders (possibly from @csallen?): "The best way to come up with a business idea is to start a business."

Inspiring article. I read an article on lemlist the other day, about refusing external funding. I'm wondering if he got he inspired by Mailchimp.