You’re probably already aware that you can save any partially-composed e-mail messages as drafts in the iOS Mail app—these messages go to a “Drafts” folder on your device and you can find them there simply by accessing it via your folder list. However, iOS 6 adds a cool new hidden feature that allows you to access any of your draft messages more quickly, right when composing a new message.
Simply tap and hold on the Compose button in the bottom right of the Mail app and a quick list of all available drafts in your mailbox will appear, along with a button at the top to create a new message should you choose to do that instead.
You can even swipe-to-delete from here to remove any drafts that you no longer need.