The Wooden Border Stencil is a two-piece tool that is laser cut from a thin piece of wood. It can be used in several different configurations to create old-timey borders on your envelopes.
You can stencil an outer border, an inner border, and three address lines. Stenciling all three elements on one envelope gets a bit busy. My preferred style is a single outer border with address lines.
Another solid approach is to go with a double border but skip the address lines.
You can also cheat by skipping the full address lines but using the inner stencil to pencil in some temporary visual cues.