Paul Graham has commented about his email use: "Email was not designed to be used the way we use it now. Email is not a messaging protocol. It's a todo list. Or rather, my inbox is a todo list, and email is the way things get onto it. But it is a disastrously bad todo list."

PG's Frighteningly Ambitious Startup Ideas has #2 "Replace Email". Rocketr could have riffed on this idea, ideally researched ahead of time more about what PG wants and needs, and made the pitch more compelling.

A related suggestion is to show how Rocketr may relate to other companies that Y Combinator knows well, such as their own investment portfolio. If I recall correctly Siasto/Taskforce is doing productivity tools and combines emails, tasks, notes, and projects quite well.