A mailbox mounting bracket is configured for attachment to a post, rail, fence, or the like, to allow a mailbox to be mounted in multiple orientations. The bracket has a top plate with a plurality of holes for mounting to the bottom of a mailbox, a downwardly-extending peripheral ridge with a plurality of holes for mounting to the sides of the mailbox, and first and second downwardly-extending flanges at opposite sides of the bracket each with a plurality of holes for mounting to opposite sides of the post, fence, rail or the like. In another embodiment, the bracket includes two pieces each having a top plate, the top plates being rotatably connected to each other for extra support and versatility.