I don't know that these really need much explanation. Letter boxes in doors (two from France) and letter boxes (post boxes) where you leave your letters for collection.
In my enthusiasm for old doors I find I have several letter boxes. This one was in Canterbury where a house was being renovated.
The Royal cipher, GR, shows that his wall box is a George V 1910-1936 box.
From France, a letter box in a red door.
This one is a Victorian letter box at the historic dockyard in Gloucester. I don't know whether it applies in this case, but some of the older boxes have been listed in the same way as protected buildings.
Finally, from France, a letter box in a very old door. Letter boxes in doors are very common in the UK but much less so in France.
I'm tempted to go into details about the different types of post box: pillar boxes, wall boxes, lamp boxes, but I think I'll stop while the going is good.
This is yet another very late entry for this week's Photo Hunt. Visit TNchick's site where you can find more people who have joined in at a more reasonable time.
PS Part of the reason I'm so late posting is because it's taking me at least three times as long to create a post because of some Blogger problems: uploading pictures takes forever and line or paragraph spacing goes crazy at the drop of a hat.