This is a nice photo, and it was adventurous of you to attempt a panorama on DPCs limit 640 pixel budget.
Aesthetics: This is a good theme, with a nice feel to it. Tones are good. Composition is good horizontally but less so vertically. I think the mailboxes are too centered on that axis. Also, there's not much punch to the geometry here. It works on the expanse theme, but that wears quickly. Looking down the line with perspective might have been another interesting approach. The current view is especially problematic at this resolution, since the boxes end up being so small. A tilted shot running the diagonal might have also been interesting. Or laying down on the ground in front of them, against the sky, wide angle lens, is another thought.
Technical: Hard to see here, but sharpness appears good, and tones are excellent.
Nice use of wide angle. Found the subject to be generally too busy. The centering of the mailboxes also cause the image to be too split in half. I do like the way the sky looks, though, and the contrast of the mailboxes was pretty good.
I think this image lacks punch. For this to successfully relay it`s message, I believe that moving closer to the mailboxes and maybe just focusing on a few or shooting them so that they are in line would be more effective.
You may get comments on it being too small, despite the fact you used 640 pixels wide. I ran into that a few weeks back with a 640x213 image. But you won't hear it from me. I like it. Although, I may have had the mailboxes a little lower and shown more sky.