You may want to aggressively filter the amount of emails you're going to index, then. It's not rare that people have inboxes bigger than 10Gb. To be honest, I

You may want to aggressively filter the amount of emails you're going to index, then. It's not rare that people have inboxes bigger than 10Gb. To be honest, I think email search is something even Google hasn't succeeded yet. The way it's introduced on your homepage makes me think you have succeeded...but it will definitely be HARD to scale if your service becomes popular.