I have a pretty deep relationship with the post office as it seems (very thankfully!) I spend half my preparing boxes to bring them, and I still find it amazing that one can just put something in the mail and have it be carried across the globe! And so, of course, I lit on this immediately when I found it in Maine the other day--19th c., tin, painted black with stenciled lettering reading (more or less) "Post Office Delivery." I assume likely this would have hung in the lobby of a multi-tenant building, with enough slots to accommodate a fair bit of mail. And it would be nice and useful still hung near the front door for outgoing mail--which most contemporary mailboxes really don't seem to account for very well! 

7 1/2" x 4 1/2 x 6 1/8" t. Plenty of wear and paint loss as evident, which just makes me think of the intrepidness of postal workers, rain or shine!  Structurally sound and with two holes for hanging.