Mailbox Specifications


Michigan's state and local road agencies follow the standards published by the American Association of State Highway and Transportation Officials (AASHTO) in "A Guide for Erecting Mailboxes on Highways."

  • Only one support should be used per box or group of boxes;
  • Wood posts should be no more than 4 1/2 inches diameter if round, 4x4 inches if rectangular;
  • Metal pipes should be standard steel or aluminum with no more than a 2 inch inside diameter;
  • Supports should yield or collapse if struck.  They should bend or fall away from a vehicle and not create a severe deceleration;
  • Supports cannot be fitted with an anchor plate (metal post), embedded over 24 inches into the ground, or set in concrete;
  • The mailbox must be constructed of sheet metal, plastic or similar weight materials, with weight not to exceed 11 pounds;
  • The United States Postal Service asks that roadside mailboxes be 36 to 42 inches off of the ground, and 8 to 12 inches behind the shoulder or the curb;
  • A mailbox and its support will be considered hazardous to motorists when the support exceeds the described structural imitations; and
  • Any mailbox and its support considered to be a hazard should be removed from the road right-of-way and replaced.


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