Narrated by John Grierson and Stuart Legg, the film ends with a "verse commentary"[1] written by W. H. Auden to a score composed by Benjamin Britten.

In 1933, Stephen Tallents left his position as a secretary and director of the Empire Marketing Board (EMB), a government advertising agency that decided to cease operations, and began work as the first Controller of Public Relations for the General Post Office (GPO).

The liberal-minded Watt, Wright, Grierson, and other GPO film unit members, therefore, wanted Night Mail to focus not only on the efficiency of the postal system but its reliance on its honest and industrious employees.

[10] The script developed, a film crew was assembled that included Wright, Watt, and cameramen Pat Jackson, Jonah Jones, and Henry "Chick" Fowle.

[16] The GPO secured a £2,000 budget for the film's production,[9] and calculated staff travel allowances by the accounts department totalling the salaries of the crew involved and setting aside money based on the figure.

[19] The on screen individuals were real life postal employees, but their dialogue was originally written by Watt and Wright who gained inspiration from the conversations they overheard while observing them at work.

With the processed film ready in the morning, Jackson would take a postal train back to Crewe where the team could view the footage at a local cinema before it opened at 2:00 pm.

To solve this, Jackson sat atop of the coal pile in the locomotive's tender while holding a reflective sheet made with silver paper that acted as a mirror to make subjects brighter.

Watt expressed his disagreement with the idea at first, but came round to it when it presented the opportunity in shooting additional footage and using previously shot film that was could not be used to complete the sequence.

Many lines from the original version were discarded and became "crumpled fragments in the wastepaper basket",[36] including one that described the Cheviot Hills by the English–Scottish border as "uplands heaped like slaughtered horses" that Wright considered too strong for the landscape that was shot for it.

"[37] The sequence begins slowly before picking up speed, so that by the penultimate verse, assistant and narrator Stuart Legg speaks at a breathless pace, which involved several pauses in recording so he could catch his breath.

[5][41] Watt urged Britten to avoid "any bloody highbrow stuff", and showed him the picture while playing an American jazz record and requested "this kind of music".

[5] He was allowed an orchestra of ten musicians, and used a compressed air cylinder and sandpaper to create a "sound picture" of the pistons and pumps of a steam locomotive at speed.

[43] In order to keep the orchestra in time, Britten conducted to an "improvised visual metronome" that involved marks cut at particular intervals in the film that appeared as flashes on the screen.

[46] Jackson, Watt, and Wright were among the GPO staff present; the former recalled the audience's enthusiastic response to the film which included an "enormous applause" at the end.

The GPO commissioned posters, special screenings, and other soft publicity opportunities, taking advantage of the glamorous image and popularity of railway films to promote Night Mail.

Unlike other GPO films, which were primarily screened in schools, professional societies, and other small venues, Night Mail was shown in commercial cinemas as an opening for the main feature.

"[54] In The Morning Post, a reviewer believed that Night Mail's achievement was obtaining "natural acting from the railway and postal officials concerned, as it is extremely difficult to prevent people from 'putting on their best behaviour' when they know they are about to be photographed".

[55] Tallents praised Night Mail highly, as it "Had no snob appeal, making falsely glamorous and desirable to humble people the fundamentally commonplace and vulgar luxuries of the rich.

It took as its raw material the everyday life of ordinary men and from that neglected vein won interest, dignity and beauty [...] and struck a more universal note.

"[56] According to documentary author Betsy McLane, Night Mail makes three primary arguments: First, the postal system is complex and must function under the auspices of a national government in order to thrive.

[58] He cites Night Mail’s portrayal of the postal system's practical and symbolic importance through both humanistic realism and metaphorical imagery as characteristic of Grierson's ideals.

Author A. R. Fulton points out effective film editing to build suspense on everyday operations, such as the mail bags being caught by the track side nets.

First, Night Mail portrays the daily activities of the postal staff on a human scale, with colloquial speech and naturalistic vignettes, like sipping beer and sharing inside jokes.

Second, Night Mail uses expressionistic techniques like heavy back lighting and the lyric poetry of Auden to convey the grand scale of the postal endeavour.

This ancillary commentary serves to elaborate on the onscreen action (“The pouches are fixed to the standard by a spring clip”) or invigorate and expand the world of the film (“Four million miles every year.

In contrast to previous GPO releases, Night Mail garnered critical notice and commercial distribution through Associated British Film Distributors (ABFD).

[63] English television producer and author Denys Blakeway praised Auden's contributions and the coda sequence which "rescued the documentary from plodding Post Office propaganda and helped to establish the emerging form as a new branch of the arts".

The piece, entitled Crossings, was described by author Scott Anthony as "considerably less believable" than the original Night Mail and comes across as "a cuttings job.

[70] The opening stanza of the poem was sampled heavily by electronic musician Aphex Twin, under his AFX moniker, in the song Nightmail 1, officially released by Warp in July 2017 as part of the orphans digital EP.