It's a USPS dropbox ("Owens" style)that may have a maker embossed on the sides and/or a date on the bottom. It's missing the upper frame across the front and the lower schedule frame that goes where the someone tried their hand at schedule lettering. Can't tell, but most are cast iron. I have two, one like that that's dated 1930 for comparison and an older version (1910), different style. It should also have a two piece mounting bracket on the back. One piece bolts to the box, the other bolts to the pole or wall and then the box slides over it and locks in place.
The lamp is what it is, a lamp.
