Something like 350B emails are sent every day (!) but no one I know is all that satisfied with email as a platform. Complaints I hear most often are spam / lack of verified identity, threads getting unwieldy after many messages, formatting annoyances, and not enough fine grained control over notifications. If you could change one thing about email to make it awesome, what would it be?
Success and failure can mean different things to different people, and it's important to define what those terms mean for you and your work. What is your definition of success and failure in your work?
