Curbside Mailboxes: A Chronology of Size Changes

1896: Rural free delivery (RFD) began as an experiment. Some customers used homemade wooden boxes as mailboxes, while others used old cigar boxes, soap and feed boxes, drainage pipes, sections of stovepipe and other salvaged items. Many farmers were reluctant to invest in fancy new mailboxes while RFD was an experimental service.

1901: Concerns about the security of mail prompted the Postmaster General to appoint a committee to examine and recommend specific models of mailboxes for use on rural routes. It was thought that mail deposited in officially approved boxes would be better protected from both weather and theft.(1) First, the committee agreed upon basic requirements for rural mailboxes, including:

1. All boxes had to be "of metal, galvanized iron, or steel with openings and hinges so constructed as 
    to be impervious to weather";
2. Boxes were to be "approximately 6 by 8 by 18 inches"; an opening at the side or top was preferred;
3. Each box had to be fastened to a post "at such height . . . as to be easily opened and inspected by 
    the carrier without alighting."(2) 

The committee examined 63 mailboxes that had been submitted for review and approved 14 of them. While customers were not required to remove existing mailboxes, only approved mailboxes were permitted on new routes or when replacing old boxes — a policy that continues to this day.    

1902: RFD became a permanent service. The Postmaster General appointed a committee to investigate if a suitable mailbox could be purchased in bulk for 50 cents or less and sold to rural patrons at cost. While the committee could not find a suitable box at that price, it did fine-tune the requirements for approved boxes. It specified that boxes be constructed from at least 20 or 22 gauge galvanized sheet metal, and reduced the minimum size for rectangular boxes to 18 by 6 by 6 inches, while specifying a minimum size of 18 by 6 inches for cylindrical boxes. Any manufacturer could make mailboxes, but all boxes were required to conform to the new specifications to receive approval.  Approved selections — marked "Approved by the Postmaster General" — varied widely, since samples of boxes were inspected by special agents in 14 different sections of the country, who sometimes interpreted the rules differently.  
  
1913: Parcel Post was introduced. Many rural mailboxes could hold only the smallest packages. One Maryland carrier complained that some boxes on his route were not big enough to hold a mail order catalog, let alone merchandise. If a package was too big, and the customer did not live within hailing distance, carriers were instructed to leave a notice in the box asking the customer to meet him at the mailbox the next day. This system was not ideal — carriers sometimes hauled around the same packages for days. To accommodate Parcel Post, a committee appointed by the Postmaster General to recommend a standard rural mailbox chose one measuring 24 inches long by 11 inches wide by 13 ¾ inches high, but no order was issued changing the 1902 specifications.  

1915: The Post Office Department adopted two standard mailbox designs and provided detailed drawings for each. The smaller box, No. 1, at 18 ½ inches long by 6 ¼ inches wide by 7 ½ inches high, was similar in size to previously-approved models. The larger box, No. 2, at 23 ½ inches long by 11 inches wide by 14 inches high, was similar to the one recommended by the mailbox committee in 1913 and was intended for "regular mailers of Parcel Post."(3) Both boxes were tunnel-shaped, one of the most popular styles of box on the market due to its simple construction and inherent weather resistance. Any manufacturer could make the mailboxes, but only compliant models received approval. Effective July 1, 1916, only these new boxes could be installed along rural routes, as well as along contract routes that provided box delivery.

1929: Because of increasing amounts of Parcel Post and "the inadequacy of the existing type of rural mail box," the Department adopted the No. 2 size mailbox as the only approved box.(4) At 23 3⁄16 inches long by 11 inches wide by 13 3⁄8 inches high, it had more than four times the capacity of the No. 1 box.  Beginning July 1, 1929, all new rural mailboxes were required to be of this type.  

No. 2 Rural Mailbox, 1929
Specifications for the No. 2 rural mailbox were approved by the Postmaster General on November 1, 1928. 

Kirby, Vermont, 1937 (courtesy Library of Congress)
From 1929 to 1936, all new rural mailboxes were required to be the No. 2 size box, which had more than four times the capacity of the No. 1 size.

1936: The Department once more accepted the previously-approved No. 1 size box, alongside the existing No. 2 box, as an approved box. While some rural carriers lamented the reintroduction of "old toy No. 1 boxes," other carriers thought that the smaller boxes were easier to service and that customers should have the option of purchasing the smaller, cheaper box.(5)
  
1953: The Department specified the dimensions of the two approved mailbox sizes as follows:

No. 1:  Approximately 19 inches long by 6 ½ inches wide by 8 ½ inches high;
No. 2:  Approximately 23 ½ inches long by 11 ½ inches wide by 13 ½ inches high.  

1954:  The Department approved a third, medium size of the standard, tunnel-shaped rural mailbox: No. 1A, which was approximately 21 inches long by 8 inches wide by 10 ½ inches high, with a letter slot in the door. 

1956: The Department permitted deviations from the design specifications, if approved. Boxes could be any size between the allowable minimum and maximum dimensions, provided the "proportions and general shape" given in the Department's drawings were maintained.(6)    

1960:  The Department approved the modern-style "contemporary" box for rural use. This style had been used previously by suburban residents served by city routes, whose choice of mailbox was not subject to regulation. 

1962: Design drawings for the three sizes of the standard rural mailbox were reissued, largely unchanged. Requirements were developed for contemporary mailboxes and were fine-tuned six weeks later. Because so many manufacturers made contemporary mailboxes out of plastic, the Department did not specify the materials.  Also, no particular designs were specified, but only minimum dimensional capacities and door openings, and minimum requirements for strength and durability. To receive approval, contemporary boxes had to meet the following size requirements:

C1: Large enough to hold a parcel measuring 5 by 6 by 18 ½ inches (with one side of the parcel lying 
       flat on the box floor), minimum inside width at bottom 6 inches, minimum door opening of 40 
       square inches; 
C1A: Large enough to hold a parcel measuring 6 by 7 ¾ by 19 ½ inches (with one side of the parcel 
        lying flat on the box floor), minimum inside width at bottom 7 ½ inches, minimum door opening of 
       65 square inches;
C2: Large enough to hold a parcel measuring 8 by 11 ½ by 22 ½ inches (with one side of the parcel 
      lying flat on the box floor), minimum inside width at bottom 10 ½ inches, minimum door opening of 
      130 square inches.

The standard/traditional (left) and contemporary (right) approved mailbox styles were pictured in the April 21, 1966, issue of the Postal Bulletin. 
1974: The Postal Service issued USPS-STD-7, with specifications for the three sizes of rural mailboxes in both the standard and contemporary styles. The minimum interior dimensions of the medium size contemporary box were slightly reduced — this size box was now required to hold a parcel measuring 6 by 7 by 19 ½ inches. 

1985: The Postal Service reissued USPS-STD-7, with specifications for rural mailboxes in two styles — standard (renamed "traditional") and contemporary. The same three sizes were now specified for each style:

1:  19 inches long by 6 ½ inches wide by 8 ½ inches high;
1A: 21 inches long by 8 inches wide by 10 ½ inches high (with optional letter slot in door);
2:  23 ½ inches long by 11 ½ inches wide by 13 ½ inches high.    

1992: The Postal Service issued USPS-STD-7A, with specifications for "all city and rural curbside mailboxes."(7) As had been the case since 1956, the Postal Service permitted deviations from the specifications, if approved. Customers in all areas, including those served by city delivery, were now required to use approved boxes when adding or replacing curbside mailboxes. Minimum interior sizes were specified as follows:

T1 and C1: 18 ½ inches long by 5 inches wide by 6 inches high
T2 and C2: 19 ½ inches long by 6 inches wide by 7 inches high
T3 and C3: 22 ½ inches long by 8 inches wide by 11 ½ inches high
 
2001: The Postal Service issued USPS-STD-7B, with specifications for "all curbside mailboxes."(8) Traditional mailboxes were no longer required to be built according to USPS drawings. All traditional and contemporary boxes were required to easily accept a test gauge measuring 18 ½ inches long by 5 inches wide by 6 inches high when inserted with the 6-inch dimension perpendicular to the mailbox floor. Particular sizes of traditional and contemporary mailboxes were not specified, just minimum and maximum dimensions, as follows:

Length: approximately 18 9/16 to 22 13/16 inches  
Width: 6 ¼ to 11 inches
Height: 6 to 15 inches  

Also, to help address growing security concerns and reduce the use of unapproved locking mailbox inserts, the Postal Service approved a set of requirements for a new locking type of curbside mailbox. While its shape and size were not specified, the "locked mailbox" was required to meet "applicable functional requirements" and to have a slot for incoming mail that was at least 10 inches wide by 1 ¾ inches high.(9)   

Endnotes

1. Postal officials wanted better physical protection — and better legal protection — of mail. In 1901, locks were recommended for all rural mailboxes, except those that were "practically in the farmer's dooryard" (Annual Report of the Postmaster General, 1901, 122). Also, postal officials believed that mail deposited in mailboxes "approved by the Postmaster General" would be protected by a federal law with severe penalties for anyone who tampered with mail deposited in "receptacles established by authority of the Postmaster-General" (Ibid., 123; 17 Stat. 318).
2. Annual Report of the Postmaster General, 1901, 122.
3. Post Office Department statement cited in the November 20, 1915, issue of the rural letter carriers' publication R. F. D. News.
4. The National Rural Letter Carrier, December 22, 1928 (name changed from R. F. D. News in 1927).
5. The National Rural Letter Carrier, December 7, 1935; see also the December 21, 1935, issue.  Rural carriers continued to discuss the 1936 change in issues of The National Rural Letter Carrier through April 1936.
6. Postal Manual, Transmittal Letter 21, section 156.512, December 11, 1956.
7. USPS-STD-7A, "U.S. Postal Service Standard: Mailboxes, City and Rural Curbside," December 17, 1992, 1; copy in files of USPS Historian.
8. USPS-STD-7B, "U.S. Postal Service Standard: Mailboxes, Curbside," February 8, 2001, 1; copy in files of USPS Historian.
9. Ibid., 4. Note: There was no security test requirement for the new locking type of curbside mailbox.

HISTORIAN
UNITED STATES POSTAL SERVICE
SEPTEMBER 2014