Co-founders of theSkimm Danielle Weisberg and Carly Zakin talk with Peter Kafka about how they built up an email newsletter that gets opened by 1.5 million people, and why they want more. TheSkimm's mission is to make its readers (predominantly young, educated women) more informed and engaged with brand partners, and Weisberg and Zakin explain why email is just one tool to do that.