I think along with this TOY-ness, YC also looks for the available market and in this case I do not see that with this app. maybe the idea is to get some traction and sell it to Google down the road?
I maybe wrong but I see the email market in two ways: people who have two many emails which creates a scheduling problem. And people who reply/compose too many emails. I think the later market is not that big because you also need to make sure the people get more value (or should I say, write more emails) out of the monthly fees they pay for the service. But I'd like to be wrong here and I wish you succeed. Thanks.
That's certainly a possibility, but for now we're just really focused on making the product really useful.