How to Install a Door Mail Slot (and Through-Wall Slots)

Cutting a rectangle into a perfectly good front door feels risky, but a door mail slot is one of the more forgiving entry door projects when you measure twice and know what is inside the door. Most installs take an hour or two with a drill, a jigsaw and a clean template. The bigger decisions come first: whether your door can safely be cut at all, where the slot should sit, and whether a through-wall slot would serve you better.

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Solid wood and fiberglass doors with a wood or foam core take a slot well. Steel doors work too, with the right blade and some patience. Doors you should never cut include any fire-rated door, such as one between an attached garage and the house, and doors with glass or internal wiring in the cut zone. If you rent or live under an HOA, check the rules before cutting, and confirm with your local post office that the slot height and size meet their delivery guidelines.

Choosing a Door Mail Slot and Location

A standard door mail slot has an exterior plate with a spring or gravity flap and an interior trim plate or hood. Common opening sizes run from about 1.5 by 7 inches up to 3 by 13 inches. Larger openings handle magazines and small padded envelopes but let more draft through, so pair a large slot with a good seal.

Placement matters for the carrier and for your door’s structure:

• Height: most delivery guidance favors a slot no lower than about 30 inches from the bottom of the door, and a comfortable height of 30 to 45 inches is common. Very low slots are hard on carriers’ backs.
• Rails and stiles: on a panel door, cut through the solid lock rail or a flat rail, never through a raised panel or its frame joints.
• Clearance: keep the slot at least 3 to 4 inches from the lockset, deadbolt and any door edge so you do not weaken the door or hit hardware.
• Inside obstacles: confirm the interior plate and any catcher will not hit a storm door closer, a wall, or a stair rail when the door swings.

A complete door mail slot kit usually includes both plates, screws long enough for standard door thicknesses and a paper template, which saves a lot of layout time.

Check What Is Inside the Door First

Before you cut, find out what the door is made of and what runs through it. Look at the top or hinge edge of the door, read any label on the hinge edge, and check the manufacturer documentation if you have it.

• Fire-rated doors: a label on the hinge edge or top of the door indicates a fire rating. Never cut a fire-rated door; it voids the rating and compromises safety.
• Smart locks and powered hardware: doors with electrified locks, powered strikes, or integrated lighting may have low-voltage wires routed through the door. Some setups use a power transfer hinge feeding wires across the door. If the lock is hardwired, turn off the breaker for the circuit feeding its transformer and confirm power is off with a non-contact voltage tester before drilling. Battery-only smart locks do not carry hidden wiring, but still keep the cut well away from their internal mechanism.
• Glass and decorative inserts: keep clear of any glass frame by a few inches. Cutting into an insert frame can crack tempered glass or break its seal.
• Steel door core: a strong magnet will show where steel skins and any internal reinforcements sit.

Tools and Materials

• Mail slot kit with exterior and interior plates
• Tape measure, square, level and pencil
• Painter’s tape to protect the finish and mark the cut
• Drill with a 1/2 inch or 3/4 inch bit for starter holes
• Jigsaw with a fine-tooth wood blade, or a metal-cutting blade for steel
• File or rasp and sandpaper
• Exterior caulk or sealant and a small brush of matching paint or stain
• Safety glasses, hearing protection and a dust mask

How to Cut and Fit a Mail Slot in a Door

1. Remove the door if possible. Pop the hinge pins and lay the door flat on sawhorses with blankets underneath. A flat door is much easier to cut square, and you avoid chips in the jamb.
2. Mark the opening. Apply painter’s tape over the work area on both faces. Center the template on the door width at your chosen height and trace the opening. Use a square to transfer reference lines around the door edge so the outside and inside cuts line up.
3. Drill starter holes. Drill a hole in each corner of the opening, inside the cut line. Drill halfway from one side, then finish from the other side to avoid blowout on the far face.
4. Cut the opening. Run the jigsaw from hole to hole along the line. On steel doors, use a metal blade at slower speed and cut the skin, clear the foam core, then cut the inner skin from the other side.
5. Smooth and seal. File the edges clean. Seal raw wood edges with exterior paint, stain or sealer so moisture does not soak into the core. On steel or fiberglass, seal the exposed foam with a thin bead of exterior sealant.
6. Fit the plates. Set the exterior plate with the flap hinge at the top, then the interior plate. Drill pilot holes, apply a thin bead of exterior caulk behind the outer plate, and drive the screws without overtightening.
7. Test. Rehang the door and push a few envelopes and a folded magazine through. The flap should close on its own with no binding.

Many modern doors are thinner or thicker than older ones, so if the supplied screws are wrong, buy matching through bolts or sleeve screws of the correct length in the same finish.

Through-Wall Mail Slots

A mail slot for wall installation runs a chute from an exterior faceplate, through the wall cavity, into an interior plate or a lockable collection box. It is a good choice when you do not want to cut an expensive door, or when you want mail to land in a secure box inside a garage or mudroom.

This is a framing project, not a quick door cut. Keep these points in mind:

• Locate studs and services. Use a stud finder and check for wires, pipes and ducts. Turn off the breaker for any circuit in that wall and confirm with a non-contact voltage tester before cutting drywall.
• Frame the opening. If the chute sits between studs, add a header and sill blocks to create a clean box. If it requires cutting a stud, the opening needs a properly sized header; on a load-bearing wall, consult a contractor.
• Weatherproof the chute. Slope the chute slightly to the outside so rain drains out. Flash the exterior opening with flashing tape lapped shingle style into the weather barrier, then seal around the faceplate with exterior sealant.
• Air seal the interior side. Foam or caulk gaps between the chute and drywall to stop drafts and insects.

Masonry, stucco and brick walls take core drills or masonry saws, and these cuts throw silica dust. Wet-cut, wear a respirator rated for silica, or hire a mason.

Catchers and Draft Seals

A mail slot catcher, sometimes sold as a door mail slot catcher, is a wire basket or enclosed box mounted on the inside of the door below the opening. It keeps mail off the floor, out of reach of pets, and away from wet boots. Measure the catcher’s depth against the swing of the door and anything behind it, such as a wall or radiator.

Drafts are the main complaint about slots. Look for an interior hood with brush seals or a second flap. An insulated interior cover can cut winter drafts noticeably. If you are buying a new front door with mail slot already factory cut, ask whether it includes a sealed interior hood.

Troubleshooting

• Flap sticks open: the plate is out of square or a screw is overtightened and bending the plate. Loosen and adjust.
• Rattle in wind: add a self-adhesive felt or foam bumper inside the flap.
• Water getting in: the hinge is at the bottom instead of the top, or caulk is missing behind the exterior plate.
• Mail jams: the opening is too narrow for your usual mail or the interior plate edge is sharp. Upgrade the plate or ease the edge.

Cost and When to Call a Pro

Basic slot kits are inexpensive, with mid-range solid brass or stainless options and insulated hoods costing more. A handyman typically charges a modest flat fee for a door install. Through-wall kits with collection boxes cost more, and a full install with framing, siding repair and finish work can cost several times the kit price depending on the wall type.

Hire a carpenter or contractor for through-wall slots in load-bearing walls, masonry walls or any wall with wiring and plumbing in the way. Bring in a licensed electrician if a hardwired lock, doorbell, or other wiring needs to be rerouted. A door with mail slot cut by a door shop is another clean option for costly or unusual doors.