The New York City Post Office was renamed to the James A. Farley building, after our 53rd Postmaster General, in 1982.
While the Postal Service has no official motto, the popular belief that it does is a tribute to America’s postal workers. “Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds”— is not the official Postal Service motto though it appears chiseled in gray granite over the entrance of the James A. Farley building at Eighth Avenue and 33d Street in Manhattan.
The phrase comes from book 8, paragraph 98, of “The Persian Wars” by Herodotus, a Greek historian. During the wars between the Greeks and Persians (500-449 B.C.), the Persians operated a system of mounted postal couriers who served with great fidelity.
The firm of McKim, Mead & White designed the Post Office, which opened to the public on Labor Day in 1914. One of the firm’s architects, William Mitchell Kendall, was the son of a classics scholar and read Greek for pleasure. He selected the “Neither snow nor rain …” inscription, which he modified from a translation by Professor George Herbert Palmer of Harvard University, and the Post Office Department approved it.
Source: How is New York City related to famous postal quote? – Postal Posts