Back on 11 August, I blogged about this post-box - how it once had graffiti, had been cleaned, and then it had been hit again.
When I went past today, it was clean again.
Whilst I can appreciate that Australia Post has a huge number of post-boxes (14,000 or so), I doubt that at this moment, every single one of them in every corner of Australia has been vandalised. I bet if you went to some suburbs, not a single one would be touched, whilst around here, most of them have been hit. Australia Post probably has a problem in some locations - if they did a bit of data mining and mapped the problem areas, they might find that they are few and far between, and that a small number of post-boxes account for the majority of the graffiti (the old 80:20 rule).
That said, given that Australia Post staff visit their post-boxes every working day, I am at a loss as to why they are unable to target the "problem" post-boxes with an aggressive campaign of cleaning them.