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Systems at Work


The Post Office must mechanize because, if the mail volume continues to grow, it would be impossible to cope with the great flood of mail within a relatively few years, using present-day methods.
—Postmaster General Arthur E. Summerfield, 1957

Behind the Scenes

The Multi-Position Letter Sorting Machine (MPLSM)

A short, silent film showing the Multi-Position Letter Sorting Machine (MPLSM).

Employees hard at work at the stations of a Multi-Position Letter Sorting Machine.
Employees hard at work at the stations of a Multi-Position Letter Sorting Machine.

Codes and machines revolutionized the Postal Office in the 1960s. The ever-growing volume of mail drove the Post Office to introduce ZIP Codes. Machines began taking on more and more of the work of moving the mail. Postal workers using these machines could sort 30,000 letters an hour.

Since then, the pace and scale of automation in the postal system has exploded.

“Dear Congressman Smith”
From Long Island to Capitol Hill
Letter carrier collecting mail from mailbox.
Letter carrier collecting mail from mailbox.

American citizens conduct the everyday politics of the nation through the mail, in letters like this from Joe Jones in Long Island, New York, to his congressman in Washington.

Mr. Jones drops his letter in a familiar collection box, a postal worker picks up the mail, and then this piece begins to follow a new path through the system.

At the processing center in Hicksville, NY, the letter is run through a facer-canceller. By 1968, dozens of processing centers around the country had these new machines. They oriented the letters face-up, in the same direction, so the machine could cancel each stamp—automating two jobs that postal workers had done by hand for more than a century.

Mr. Jones’s letter joins hundreds of thousands of others flowing through a new Multi-Position Letter Sorting Machine (MPLSM) at the Hicksville center. Twelve postal workers sit at stations around the machine. The machine moves Mr. Jones’s letter into position in front of one of the operators, and he or she types in part of the ZIP Code for the Washington, D.C., area. The machine sorts the letter to join others headed for Washington. Within a second, the next letter takes its place.

With thousands of others, the letter is poured into a mail sack and loaded onto a train for Washington.

Employees working at stations of a MPLSM machine.
Employees working at stations of a MPLSM machine.

At the Washington Post Office, mail clerks at a second MPLSM sorts the letter for the unique ZIP Code of the U.S. Congress.

The letters delivered to the Congressional mailroom. In the mailroom, a postal worker sorts it into the boxes for congressman, and a messenger delivers it to his office. A member of the congressman’s staff reads the letter and writes a response for the congressman’s signature.

River of Mail

River of Mail is a nine-minute video produced by the Post Office Department in the late 1960s to teach the public about mail processing methods used during the 1960s and early 1970s.

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