"It's your e-mail reference library," says Trapani. It contains everything you might someday want or need. "You just don't need to separate old e-mails into different folders, because you can always search this dumping ground by sender, topic, or keyword."
This folder would be for everything that requires someone else's help. Trapani says, "Don't put stuff in your follow-up folder that you can't actually follow up on yet."
This would contain all the e-mails that you must respond to but require more than two minutes to do so. (For any e-mails that take less than that to answer, you should respond as you read them.)