Before it even launched in early 2013, more than 1 million people signed up to try Mailbox. A month later, at the height of the app’s popularity, Dropbox bought it for a reported $100 million. At the time, Dropbox CEO Drew Houston said it would help the company’s then-nascent efforts around collaboration. "Many have promised to help us with our overflowing inboxes, but the Mailbox team actually delivered," he said. "Whether it’s your Dropbox or your Mailbox, we want to find ways to simplify your life."