I suspect that's why there's a big old lap joint on the post.
That wouldn't help me much.
The first mailbox post we put up was a 4x4 treated post just like yours....but down here, the hoodlums don't settle for beer bottles (which mostly dent the box), no, they use pieces of cement blocks, bricks, and watermelons.
Our first box was white like yours and got hit with a chunk of block the first week.....it broke the post off at the ground.