Abstract: A mailbox receptacle is combined with a supporting post, on which it forms an upper portion characterized by a floor extending transversally across the interior of the tubular post at a level spaced somewhat below the upper end. A lateral opening is provided into the interior space above the floor, and a tubular sleeve is coaxially rotatably mounted on the upper end region of the structure. The tubular sleeve has a lateral opening which registers with the receptacle opening in one orientation of the sleeve. And the tubular sleeve may be rotated to fully close the receptacle opening. Stops are provided to define the angular extremes of rotary movement of the tubular sleeve, and the sleeve or a cap structure provided on the post over the sleeve may include a signal flag which, particularly in the latter case, may be caused to operate in conjunction with rotation of the sleeve in the course of opening or closing the receptacle.