USPS Relay mailbox

Relay Mailbox

Swift completion of storage

Littera excambio 


Littera excambio (cn. USPS Relay Mailbox) are the unsung workhorses of urban mail delivery. L. excambio holds a day’s worth of mail for the mail carrier, since they can only hold so much mail at one time, allowing the mail carrier to come back to their L. excambio multiple times a day. 


A medium sized box on four thin legs, with half-round top; green with the words “U.S. Mail” and Relay Mail” stamped on the front.


Primarily curbside on major USPS mail routes. 


Throughout the five boroughs.

Explore Genus Littera

  • Littera buxus
    Mail Collection Box Receptacle
    • L. buxus blavus
      Standard Collection Box Receptacle (Blue Box)
    • L. buxus localis
      Local Collection Box Receptacle
    • L. buxus beccus
      Snorkel Collection Box Receptacle
    • L. buxus prioritas
      Priority Mail Express® Collection Box Receptacle
  • Package Drop Units (PDUs)
  • Mail chute
  • Lobby Drop or Wall Drop
  • Cluster Box



According to the USPS, all collection boxes (the term of art for mailbox) used to be some form of green starting around 1909; then in 1955  street collection boxes became red, white, and blue; then When the Post Office Department was reorganized, creating the United States Postal Service in 1971, the shaded deep blue found on Littera buxis (Mail Collection Box Receptacle) and the subspecies became standardized. It is supposed that L. excambio retained the green coloring since these collection boxes aren’t meant for public use, only by authorized USPS employees.

Climate impacts

L. excambio allows for a single mail carrier to deliver more mail through smart storage. With Americans increasingly moving to more urban environments, having mail carriers walk their route rather than drive a vehicle reduces carbon emissions. At the same time, the USPS has an universal service obligation and monopoly status provided in the constitution, which has been interpreted that the USPS needs to serve all residents, no matter how far away they are. This is great from a “knit America together” policy, but has profound environmental impacts. 

Further reading

  1. USPS Document: Collection Box Colors
    PDF, retrieved 20 August 2019
  2. USPS Document: Mail Collection Boxes: A Brief History
    PDF, retrieved 20 August 2019
  3. Wikipedia: Universal service obligation and monopoly status
  4. Locating Postal Relay Boxes Using a Set Covering Algorithm
  5. New York Today: Mysterious Mailboxes
  6. Wikipedia: How delivery services work

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