Awesome subject. 🙂 Love the weathered appearance, slanted position, simple background.
It’s a very centered composition. The mailbox is facing to the left so it feels like there should be more space to the left of the mailbox than to the right. Maybe twice as much. This would allow you to incorporate the weeds in the foreground, which personally, I feel add some depth and texture; a counterpoint for your eye to go after it’s investigated the mailbox for the first time. There’s just not enough of them weeds to be of interest in this first shot.
Nice way to keep your eyes open for interesting subjects. I’ve never taken a picture of a mailbox in my entire life, I don’t think. Not as a main subject, anyway. 🙂