Abstract: A security mailbox in which the conventional single door, rural mailbox is provided with a high strength enclosure and a latching lock so that when engaged the door of the mailbox may only be opened by a key. The door may also be held in a closed but unlocked position by a sliding magnetic catch that holds the door closed without engaging the latch but allows the door to be manually urged into the fully locked position. In the closed but unlocked position the door may be manually opened by the postal carrier. The postal carrier may manually close the door so that it moves past the closed but unlocked position and engages the latching lock in the fully locked position. A dual function mounting bracket is provided which has both a set of aligned holes for mounting the mailbox to a metal post with bolts and a set of offset holes for mounting the mailbox to a wooden post with screws.