Gentry Underwood had a feeling that his startup might be making some users depressed. Orchestra was Apple’s Productivity App of the Year 2011, but users were leaving after a few months using the service. “When you start using a to-do app you say ‘I’m going to put everything in here, and I’m going to be the happiest person in the world,’” Underwood says, “but nobody ever finishes everything that’s on their list. It becomes a nagging sense of failure.” An idea grew in his mind — the “euphoric inbox,” as he calls it. He and his team would use the idea to revive Orchestra — to turn it into the first to-do app that actually makes you feel good. They instead ended up building Mailbox, a new iPhone mail app launching for free on the App Store today. While Orchestra might have changed the way you manage tasks, Mailbox ends up changing something far bigger: the way you communicate with friends, family, and coworkers every day.