“There's always been this kind of unwritten rule at Basecamp that the company basically exists for David and Jason’s enjoyment,” one employee told me. “At the end of the day, they are not interested in seeing things in their work timeline that make them uncomfortable, or distracts them from what they’re interested in. And this is the culmination of that.”

For me, the genius of Mailbox was twofold. First, using it simply felt faster than any email app I ever used. It pre-fetched messages in the background; whenever you opened it you could start dealing with the daily horror of your inbox right away. Second, using it was satisfying in a way no other email client was: every time I swiped my fat thumb on a message, banishing it to the archive, the email turned a lustrous green. Mailbox was good for dashing off quick replies, but it was best-in-class for cleaning house. Every time I found myself standing in a line, I’d open up Mailbox and positively murder my inbox. Mailbox turned you into an email assassin.