Mail Box Find
Mailbox Find is an iPhone app that uses your current location to find US blue mailboxes and displays them on a map. Mailboxes are shown in order of proximity to your current location. You can also manually enter your zip code in case the iPhone does not find your current location.
In addition, you can find Post Offices, UPS stores and FedEx locations! Mailbox Find integrates with iPhone’s Maps to display your current location and accurate route to a chosen mailbox.