This is the Night Mail crossing the border,Railway Post Offices before, but on this documentary, you can actually see them in action:
Bringing the cheque and the postal order,
Letters for the rich, letters for the poor,
The shop at the corner and the girl next door.
Isn't it fascinating? The on-board mail sorting, the clip mechanism to snatch the mail bags, the control room... oh! and the British countryside of the 30s!The poem, which is recited at the end of the documentary is by W. H. Auden. Wikipedia provides some insight about it:
As recited in the film, the poem's rhythm imitates the train's wheels as they clatter over track sections, beginning slowly but picking up speed so that by the time the penultimate verse the narrator is at a breathless pace. As the train slows toward its destination the final verse is more sedate.
I hope you enjoyed that glimpse of life on a Railway train!