A structure in flat-packable kit form to protect mailboxes from snowplow damage is provided. The kit includes four to six flat components that are stackable. Two of the components and foldable so as the be secured to each other, defining a deflection surface extending in generally orthogonal directions from a shared post sleeve. The post sleeve slidably receives a mounting post disposed between the road and a roadside mailbox, where the orthogonally oriented deflection surface blocks plowed or blown snow from impacting and demining the mailbox. The flat-packable kit may include gussets for reinforcing the deflection surface by way of the post sleeve in the assembled condition.