This pillar box on Davidson Road is of the earliest 'high aperture' design where the posting slot is right at the top instead of having the 'indicator tablet' above it. The pillar box would appear to be of the larger 'type B' size (though I'm not sure if that terminology applies to boxes of this age, or indeed if the sizes had been standardized). The slot itself is particularly small meaning you might need to find another posting box unless you can fold your post.

The pillar box has a plain door. These were used on the very first boxes dating from 1879 to 1887. Davidson Road is shown on the 1872 O.S. map as Albert Road running from the Lower Addiscombe Road (St James's Road East) to approximately this point though it is clearly not full developed. So the date seems pretty consistent with the age of the housing.