Roger R wrote:

If provision of a letter box is a requirement, now that the post office
counters have a plastic size template limiting the size for first class
minimum postage letter to a narrow slot of 165 mmm x 5 mm, perhaps we can
reduce our aperture to that size and still meet the regulation.

Isn't there a rule somewhere about not having letterbox slots in the
bottom of a door, tosave postie's back? Or did I dream that?

David