The earliest pillar boxes appeared in the Channel Islands in 1852. Jersey got them first, but Guernsey wasn't far behind: three were erected there in early 1853. The experiment was successful enough for similar boxes to be introduced in England later that year.
One of those original boxes still survives in use on Union Street, St Peter Port. This hexagonal Guernsey postbox is the oldest still in use in the British Isles. It is also unusual for its colour: other Guernsey postboxes are not red but blue.