Self-assembly?

Another late blip! This old letter box was unearthed near the door latch. Could it come from the same door? The opening is quite small - just 130mm by 40mm, which is much smaller than a modern letterbox. Envelopes were generally smaller in times past, we guess. But what was it doing in the field - was the old door just discarded over the fence, or was there a secret little house there in the past? It seems to have survived pretty well, being made from some kind of alloy, or aluminium. Perhaps it's not that old after all.

Oh, by the way, after a bit of research, a replacement mower and new hedge trimmers were ordered today, both of them 'best buy' recommendations from our friends at the Consumer Association - so, they better be good!