Following on the heels of its acquisition by cloud storage provider Dropbox, the iPhone-only app Mailbox (free) has announced that it has reached the one million user mark as part of its slow rollout of the application, which organizes email using a "to-do" style approach that essentially turns email into a checklist, with a variety of options to date or put off a window when the email will be replied to or acted on. To celebrate the user milestone, the company issued a minor update to the app that adds a "shake to undo" feature.
