The message

from James Harris contains these words:

I've seen them on doors:

1. Large letter flap with a large slot behind it so it will accept
telephone directories, small packets etc. rather than just letters
2. Inward opening
3. Weak spring so even lightweight post will drop and not get caught

but cannot find a supplier who sells them. Anyone know where I can buy
such a thing?

Mine came from the local hardware store. AFAIK they all go by the name
of letter plate.

Currently I have one that has a slot approximately 9" by 2" which
replaced one with a slot 8.5" by 1.5" which was a tight fit for things
like Yellow Pages. The later has quite a strong spring. The earlier on
relied on gravity and seemed to give some postmen a problem as it was a
matter of lifting rather than just pushing.

The upgrade seems redundant now as the last telephone directory was left
on the wall by the gate (idle sod) and the previous directory was just
pushed through a gap under the inner gate by an illiterate who couldn't
read the prominent message in front of his (or her) nose saying the
letter plate was in the gable end.

On the DIY theme are there any issues with moving the letter slot from
one part of a front door to another? For example, planning permission.
I'd like to move it from the bottom of the door to the middle so I can
catch the mail behind the door. Of course, I'd need a way to block up
the existing slot somehow.

Can't see why if the door will take the butchery unless you are in a
conservation area in which case planning might need to be consulted. I
shifted mine from a letter box hung on the back of the inner garden gate
to a hole in the gable end without consulting anyone.

--
Roger Chapman