Editor's note: Inc. magazine's 2018 Company of the Year is Bird. Here, we spotlight last year's winner.

Ben Chestnut spent 2018 surrounded by construction.

Literally: At his Atlanta home, landscaping crews spent the early fall digging up the Mailchimp CEO's yard for renovations. And figuratively: At his nearly 18-year-old email-marketing company, which Inc. last year named its 2017 Company of the Year, Chestnut is implementing overhauls both visible and not.

There are new products, hundreds of new employees, millions of new customers, and even a subtle tweak to its name (note the newly lowercase "c" in "Mailchimp"). All of which have allowed Chestnut a moment or two to rest on his laurels.

"A year ago, I feel like we were talking about things we had planned," he reflected in mid-October. "This year, it's mostly live."

It's a rare bit of visible satisfaction from a CEO who runs one of the more successful small businesses in America, but who says he's always seeking the growing pains of the next challenge. By last year, Chestnut and co-founder Dan Kurzius had seen their company reach $525 million in annual revenue, without ever taking outside investment; this year, revenue grew to $600 million. Mailchimp now claims more than 20 million customers, up from 16 million a year ago, and almost 1,000 employees, up from 700 in 2017.

Much of this growth has come from Chestnut's ongoing efforts to detach Mailchimp from its email-centric reputation. Entrepreneurs and small businesses have long relied on the company's simple, freemium email-list software to start getting the word out about their businesses. Email remains Mailchimp's dominant product--it sends more than one billion messages every day--but, in 2018, the company continued pivoting toward technologies both old (direct-mail postcards) and new (stripped-down websites, or "landing pages," and a still-developing customer relationship management system).

As for the company's beloved TinyLetter newsletter service, which Chestnut said a year ago was eventually going away: He still doesn't know exactly when, but he still intends to shut it down following some "structural" work to Mailchimp. That includes an overhaul of the company's app, which he says is unlikely to be completed in the first half of 2019.​

"TinyLetter is something that we want to get right," he says. "We have to be very careful about how we make changes to our products," but "the plan is to absorb it into Mailchimp."

Mailchimp's other new products don't have anywhere near email's popularity yet. According to the company, customers have sent 100,000 pieces of Mailchimp snail-mail, and built more than 400,000 landing pages. The latter has yielded a partnership with Square, and is Mailchimp's most popular new offering--to Chestnut's surprise.

"I thought it was a dumb idea. I fought it to the end," he says. "The team just kept saying, 'Ben, you don't know what you're talking about. Customers are asking for this.'"

Chestnut let himself be overruled, a sign of the necessary evolution facing most founders of fast-growing businesses. Mailchimp's first several years were scrappy and tenuous, with Chestnut and Kurzius involved in every decision. "I knew exactly when stuff was going live, and I knew exactly what to say and what to celebrate," he reflects.

But almost two decades in, with a thousand employees depending on him and his efforts to transform Mailchimp into an even bigger marketing-software company, Chestnut is learning to let go of the small stuff.

"Great things are happening, but my hands are not on the steering wheel as much," he says. "It's a relief. It's so much detail, it's so hard to remember, and the team has just got it. And it's freed my time to think about next year."