Your mailbox is not upright. It hangs to the right.
I find the light at the bottom distracting. The highest contrast lays at the bottom. Your main subject what I expect is the mailbox comes in second place.
I would have taken a different time so that the light did not make the mark at the bottom.
Next i find the overall not contrastly enough (to gray). I know why, because when you add a grade, the bottom sand will become white.