This startup is doubling down on the idea that businesses can get customers to buy things without ever leaving their inbox

Strelka Institute for Media, Architecture and Design/Flickr

• Rebel, formerly called Rebelmail, is an email-centered marketing company that lets businesses engage with customers without ever having to leave their inbox.
• The company's most recent seed round closed at $5 million. 
• Rebel has plans to use the funding to expand its enterprise offerings.

Opening your inbox shouldn't be a static experience. This is the fundamental belief of Joe Teplow, CEO and founder of the New York-based email marketing startup Rebel, who, for the past four years has been working on creating marketing tools tailored to the inbox experience. Rebel's platform lets companies interact with their customers without ever leaving the confines of their inbox.

The company has caught the attention of investors as well. Rebel recently raised $5 million in a seed round that included Courtside Venture Capital, Sinai Venture Capital, and Wisdom Venture Capital. The company previously raised a $2 million seed round in 2014.

Teplow said that Rebel will use the new funding to expand its enterprise offerings.

"Our thesis is that the inbox is only going to get more and more interactive," Teplow told Business Insider. "It's not going the other way."

For Teplow and his team, the inbox isn't simply a fixed messaging system. "We see the inbox as an extension of applications," said Teplow. "It's one of the most powerful online environments today."

Teplow works with heavyweights like Home Depot, eBay, WeWork, and Diane von Furstenberg. Using his company's enterprise-focused platform called Rebel Shop, clients can provide interactive inbox experiences that let users take retail-based quizzes, browse luxury goods, and make purchases all within an email itself.

In the past, Rebel has been described as "the holy grail" of email marketing: A one-stop shop for companies to capture customers' attention and turn it into a profit.

One of Rebel's chief selling points is that it's relatively more affordable when compared to other online marketing campaigns. "It costs you virtually nothing to deploy a message," said Teplow. "Email is a consistent, influential means of deploying marketing."