A double mailbox post holds two curbside mailboxes on one support, usually with a horizontal spreader bar or crossarm. It is the standard fix for a shared driveway, a duplex or two houses on a cul-de-sac. The easiest route is a complete double mailbox package, which includes both boxes, the bar and the post, sized to work together.
The same approach scales to triple, quad and quint posts for three to five households. This guide covers when a shared post makes sense, the USPS and roadside rules to check first, how to lay the boxes out, and which packages we recommend.
When a shared mailbox post makes sense
- Shared driveways: two or three homes off one private drive, where the carrier stops once at the road.
- Duplexes and side-by-side townhomes: one post, one box per unit, a matching look.
- Cul-de-sacs and short private roads: grouping the boxes at one spot means one stop for the carrier and one tidy installation.
- Replacing a tired row of mismatched boxes: one clean installation instead of four leaning posts.
For larger groups and new subdivisions, a cluster box unit is usually the better fit, and USPS names centralized delivery as its preferred mode for new developments. See our cluster mailbox (CBU) buying guide.
Double, triple, quad and quint posts compared
| Configuration | Typical use | Shop |
|---|---|---|
| Double (2 boxes) | Duplex, two homes on a shared drive | Double mailbox posts |
| Triple (3 boxes) | Three homes on a private road | Triple mailbox posts |
| Quadruple (4 boxes) | Fourplex, small cul-de-sac | Quad mailbox posts |
| Quint (5 boxes) | Five homes, small rural group | Quint mailbox posts |
USPS rules for multiple mailboxes on one post
Each mailbox on a shared post is still a curbside mailbox, so the normal rules apply to every box.
- Approved boxes: each box must be an approved curbside model (look for the Postmaster General's seal) or a custom box your postmaster approves.
- Height and setback: USPS asks for 41 to 45 inches from the road surface to the bottom of the box or point of mail entry, and 6 to 8 inches back from the curb (USPS mailbox guidelines). A side-by-side row keeps every box in that range; stacked boxes usually cannot, so ask your postmaster before stacking.
- Address on every box: each box shows its house number. If the box is on a different street from the house, USPS asks for the full street address. Rural route box numbers must be at least 1 inch high in a contrasting color (DMM 508).
- Clear approach: the carrier must reach every box from the vehicle. Keep the row short enough to serve from one stop, and keep it clear of parked cars and snowbanks.
- Safe supports: USPS points to Federal Highway Administration advice that supports should bend or fall away if hit, and that posts should be buried no more than 24 inches deep.
Do not confuse a shared post with a shared box. The DMM does allow up to five families to share a single receptacle under a route-and-box address with a signed notice to the postmaster, but most households want their own locked box.
Check state and local roadside rules too
Mailboxes on public roads also fall under state DOT and local rules, which can be stricter than USPS. Florida DOT's mailbox standard, for example, says no more than two mailboxes may be mounted on a support structure unless the arrangement has been crash tested, and sets its own height range (FDOT Index 532). Check with your county or state highway office and your HOA before buying a triple or larger post for a state road. Your local postmaster has the final say on placement, and always call 811 before digging.
Layout tips for double and multi-box posts
- Keep the boxes in one row, fronts aligned. The carrier should reach each door from the same stop.
- Use the bar made for the boxes. Spreader bars are drilled for a specific box's hole pattern. A matched package avoids drilling and mismatched widths.
- Plan the width. Mail Boss spreader bars are 20 inches wide for two boxes, 33.75 inches for three and 47.5 inches for four. Make sure the row fits the space between the driveway and any obstacle.
- Label clearly. Put each house number on its own box, facing the road, so mail does not go in the wrong box.
- Agree who owns what. Neighbors sharing a post should agree in writing who maintains the post and who replaces it after damage.
- Add an outgoing-mail plan. Locking boxes may need a separate outgoing slot or a flag; check each model.
Our recommended multi-mailbox packages
Mail Boss Double, Triple and Quadruple Mail Manager: locking steel
The Mail Boss Double Mail Manager Locking Mailbox and Post includes two Mail Manager mailboxes (each with a vandal-resistant flag and 3 keys), a 2-box spreader bar, a Mail Boss in-ground or surface-mount post and the installation hardware. Each box is 11.25 x 10.75 x 21 inches, made of 14 and 16 gauge electro-galvanized welded steel, with a 12-disc wafer lock and patented anti-pry latch. The baffle door takes mail bundles and small packages up to 3.5 inches high by 10.2 inches wide and prevents fishing.
The Triple and Quadruple Mail Manager packages use the same boxes on a 3-box or 4-box spreader bar and one post. For more parcel room, the Double, Triple and Quadruple Package Master packages follow the same pattern with Mail Boss's larger package box.
Best for: shared driveways where mail theft is a concern and every household wants its own key.
Salsbury Double, Triple and Quadruple Mail Chest: aluminum, front and rear access
Salsbury's Mail Chest packages use all-aluminum mail chests with front and rear locking doors (2 keys per door, keyed alike), a non-locking front panel where the carrier deposits mail, an outgoing tray and an adjustable red signal flag. They come with an in-ground or surface-mount post option and are listed as USPS approved. The Salsbury Quadruple Mail Chest Mailbox Post Package serves four homes. Salsbury's Roadside / Designer packages are the smaller-box version, in double, triple and quadruple.
Best for: rust-prone coastal or snowy areas, and roads where you want to collect mail from the yard side.
Whitehall Multi Mailbox Capitol packages: decorative aluminum, up to five boxes
Whitehall's Dual, Triple, Quad and Quint Capitol packages use sand-cast aluminum Capitol mailboxes, 9.7 x 13 x 20.4 inches each, with a decorative post. The Quint package includes five mailboxes, the post and five door panels; its post measures 74.94 inches long by 77.75 inches high. These are listed as approved by the Postmaster General. The decorative post goes over a 4 x 4 wooden post, which you supply along with cement. They are not locking boxes.
Best for: HOAs and private roads where appearance matters more than locks.
What about Mayne multi-mail posts?
The Mayne double posts we have listed (Rockport and Newport Plus) are discontinued, so we do not recommend them for new projects. If you want a plastic post over a 4 x 4, ask us about current options.
What we learned from shipping multi-box posts
Doubles are our most common shared post. Quads have outsold triples since 2023. A few things are worth knowing before you order:
- Mail Boss stops at four. Some locking boxes weigh over 40 pounds, so a Mail Boss post will not take five. Five households can use a triple and a double, or a quint package from another brand.
- Expect more than one delivery. Boxes, post and spreader bar can arrive in separate cartons on different days. Check every tracking number before reporting a missing bar.
- Sort the bolts. A Mail Boss double includes low-profile bolts that attach the spreader bar to the post so the boxes sit flat, and standard bolts that attach the boxes to the bar.
- Each household gets its own keys. Every box has three keys, unique to that box.
- You can grow later. A double can become a triple with a 3-box spreader bar and one more mailbox.
Installing a multi-mailbox post
A loaded quad post carries four boxes plus the bar, so installation matters more than with a single box. Set the post plumb, check that the bar is level, and measure the mail-entry height of every box against the 41 to 45 inch range before the concrete sets. Our mailbox installation guide walks through the steps.
Shared mailbox post questions
We are building a brick enclosure for five boxes. What should we buy?
Five mailboxes and the spreader bars you need, without a post. Check the plan with your postmaster first.
Can two houses share one mailbox post?
Yes. Neighbors commonly share a double post with one box each. Each box must be an approved model at the right height, show its house number, and be accepted by your local postmaster.
How far apart should mailboxes be on a shared post?
USPS sets no fixed gap. Use the spreader bar designed for your boxes, keep fronts aligned in one row, and leave room for every door and flag to open fully.
Can I stack mailboxes on one post?
Ask your postmaster first. USPS wants the box bottom or mail entry at 41 to 45 inches from the road, which stacked boxes usually cannot all meet.
How many mailboxes can go on one post?
Packages go up to five. Some state DOTs limit public-road supports to two boxes unless crash tested, so check state and local rules before a triple or larger post.
Who pays for a shared mailbox post?
The households sharing it. USPS expects customers to buy, install and maintain their own curbside boxes and supports. Agree in writing who maintains the post and who pays after snowplow or vehicle damage.
Shop multi-unit mailboxes
Browse all multi-unit mailboxes, from double to quint. Need a mix of box types or a larger group? Contact us with the number of homes and we will suggest a setup.
******It is always recommended to contact your local postmaster prior to installation. While most of our mailboxes are USPS-approved your local postmaster may have specific preferences in terms of mailbox types and installation location******