An adjustable mail slot insert may include two top frame members connected to one another and two bottom frame members connected to one another. Each bottom frame member may include a side leg and a bottom leg. Each top frame member may include a side leg and a top leg. One top frame member may be connected to one bottom frame member and another top frame member may be connected to another bottom frame member. The insert may be adjustable in a horizontal direction and a vertical direction through movement of the frame members relative to one another.