Mailbox CEO Gentry Underwoods speaks last October at Thinc Iowa in Des Moines.

Last October, Gentry Underwood took the stage at Thinc Iowa to discuss why approaching problems like a designer is crucial for entrepreneurs. He touched on tolerating uncertainty, the importance of focus, and identifying the “why” of your product. Plus, he teased his new iOS-based email client, Mailbox.

A lot can happen in seven months. Since then, Underwood has launched Mailbox, filled 1 million reservations within the first six weeks, and sold the company to Dropbox, reportedly for around $100 million.

“It’s been an absolute whirlwind,” Underwood said. “Most of my experience has been like holding on to the back of a truck while it flies around corners.”

At 3:25 p.m. Friday, Underwood will join The Big Series again—this time in Omaha—to explain how Mailbox found its product-market fit and managed to scale in such a short period of time.

“I feel like we were spending all this time reconfiguring a sail in lots and lots of different ways to try and make it just the right shape to catch wind.” Underwood said. “All of a sudden, the boat started flying.”

You’ve probably heard of Mailbox. Heck, maybe you even waited in a virtual line behind hundreds of thousands of other impatient iPhone owners just for the opportunity to use Mailbox. But for the uninitiated, here’s the gist: Mailbox is the evolution of mobile email. By providing a stripped down interface, gesture-centric controls, and a cloud-based mechanism for deferring your email (the service’s killer feature), Underwood and his team crafted an app that already changed the way we use email.

Mailbox wasn’t an overnight success, though; Underwood actually sees it as the second iteration of their social-centric to-do app Orchestra. But when his team realized that people used email as a clunky, disorganized abyss for abandoned tasks, they saw a market gap to fill.

“People use email as a collaboration tool. They trade all kinds of life and work tasks, and yet the tool was never designed for that,” Underwood said. “That creates this feeling of friction and heaviness and dread around something that really should be light.”

Mailbox started with only 13 people—pretty lean for transforming an aging communication platform. But by honing the focus aspect of Underwood’s think-like-a-designer concept—launching only on iPhone, only with Gmail, and tabling a lot of conceptual features—the team created the lightweight mail client they dreamt up months ago.

“By keeping ourselves limited to just one email platform and one device, it allowed us to spend as much time and energy as possible making the experience right,” Underwood said.

Then came the flood of signups. Then the rush to scale.

Mailbox’s success garnered the attention of venture capitalists and buyers alike. But they wanted a partner, not just funding. “I knew that if we simply took money, there was a good chance we wouldn’t be able to scale fast enough to actually take the market before one of the big boys just copied our design,” Underwood said.

They landed with Dropbox, which provided them with engineering resources, customer support, and a motivated office culture—they announced the acquisition on a Friday and moved in Monday.

But most importantly, Dropbox shared Mailbox’s “why” concept: taking the pain out of work.

To hear Gentry Underwood and other inspiring entrepreneurs share their stories, tune into the Big Omaha live stream this Thursday and Friday. Tickets are still available here, or you can tune in for our live stream.

Credits: Photo by Anna Jones and Phillip Harder. Video from dropbox.com.