“The mail must go through” (postal service adage)

“The mail must go through” is a phrase that exemplifies the hardships and successes of 19th century mail carriers, such as the pony express (1860-61). The saying was popularized by America poet Joaquin Miller (1837-1913) in his July 4, 1885 poem at Woodstock, Connecticut, “Greeley’s Ride with Hank Monk.” The phrase “the mail must go through” was used three times. The poem was printed in many newspapers.
   
 
Wikipedia: Joaquin Miller
Joaquin Miller was the pen name of the colorful American poet Cincinnatus Heine (or Hiner) Miller (September 8, 1837 – February 17, 1913), nicknamed the “Poet of the Sierras”.
 
Chronicling America
1 August 1885, Sacramento (CA) Daily Record-Union, pg. 6, col. 2:
GREELEY’S RIDE WITH HANK MONK.
The following poem was ready by Joaquin Miller at the Fourth of July celebration at Woodstock, Conn.:
 
The old stage drivers of the brave old days!
The old stage drivers with their dash and trust!
These old stage drivers, they have gone their ways,
But their deeds live on, though their bones are dust:
And still many a camp-fire tale is told
Of these daring men in the days of gold.
(...)
Sat vowing the man and the mail must “go through
On time,”
(...)
With just one thought that the mail must go through;
(...)
The mail must go through with its message of love.
 
Chronicling America
26 October 1889, Los Angeles (CA) Herald, pg. 2, col. 2:
The venturesome mail carrier said that she knew the ford was dangerous, but thought that the mail must go through at all hazards.
 
Chronicling America
16 January 1895, Anaconda (MT) Standard,  “Dare-devil Mat,” pg. 6, col. 3:
“If there is any possible chance to get over,” said she, “I intend to cross, come what may, even if I have to swim the creek. The mail must go through.”
 
6 March 1905, Colorado Springs (CO)

, pg. 8, col. 3 ad:
Swiftly as the Mail
The U.S. mail must go through quickly and on time.
(Ad for the Santa Fe railroad—ed.)
 
Google News Archive
24 May 1923, The Mount Airy News (Mount Airy, NC), pg. 4, col. 3 ad:
“WAY for the United States mail!” Men have suffered, sacrificed and died in order to expedite the country’s mail. In fact, the mail become a symbol not unlike the flag itself; whatever else happens, the mail must go through.
(Standard Oil Company of New Jersey—ed.)
 
OCLC WorldCat record
The mail must go through : the Denver Public Library presents William E. Barrett ...
Author: William E Barrett; Denver Public Library.
Publisher: [Denver, Colo.] : The Library, ©1943.
Series: Speaking of wings, no. 18.
Edition/Format:   Book : English
 
OCLC WorldCat record
The mail must go through! : a story of the Pony Express
Author: Alan James; Richard Osborne
Publisher: Kenosha, Wis. : S. Lowe, ©1949.
Series: Swap-it books.
Edition/Format:   Book : Fiction : Juvenile audience : English
   
OCLC WorldCat record
Seven little postmen : story and song.
Author: Margaret Wise Brown; Larry Groce
Publisher: [Burbank, Calif.] : Disneyland, ©1976.
Series: A Disneyland storyteller cassette
Edition/Format:   Audiobook on Cassette : Cassette recording : Fiction : Juvenile audience : English
Performer(s): Story, Margaret Wise Brown ; song, The mail must go through, Larry Groce.