How To Make And Install a Curbside Mailbox Post

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Build your own mailbox post.

Email and texting have all but eradicated hand written letters. But your home still needs a mailbox. After all, who’s heart doesn’t pitter-patter at the sight of bills and other junk mail? Mine sure does! Plus it provides the bulk of my recycling bin’s daily fiber intake. In related news, I need to upgrade my ratty old blow-molded mailbox to something a little more substantial. If you’ve ever wanted to build and/or install your own curbside mailbox post, we’re going to walk you through the process.

Wait A Minute, Mr Postman – It’s Time For A New Mailbox

Out With The Old
This puny plastic mailbox just isn’t cutting it for me. And for some reason, small wasps keep building nests in the front door handle. It’s happened 4 times now and it’s not cool. (It’s a miracle neither I nor the postal workers have been stung!)

When I’m not writing for Home Fixated – or doing “independent QC” on assorted microbrews – I can be found hunting unique and collectible items to resell online. For days when there are only a handful of orders going out (and/or nothing that’s really big), a larger mailbox would save me a trip to the post office. So I stepped up to Gibraltar’s extra-large capacity ST200B00. Up close, this thing is almost comically large, but it’s exactly what I need.

The post we’re building today works with mailboxes of any size, whether your child can fit in it or not. The core project consists of three main parts: a tall vertical post, a horizontal mailbox “support arm” and a diagonal brace. Depending on the mailbox you choose, you may also need to add a flat mounting platform.

Note that the United States Postal Service (and probably whoever carries the mail in your neck of the world) has regulations regarding curbside mailboxes. These postal regulations and requirements are worth a careful read.

Mail Wood And Hard-ware – Hunting And Gathering

6 foot & 8 foot PT 4x4's
This wood was wet and sticky at first. I let it dry for a few days before starting the project.

Our journey begins with a trip to the home center. In addition to the materials listed below, you will need hardware to attach the mailbox. And, if you want the mailbox to sit on a platform, wood to make said platform (I trimmed a scrap of 2×12 for mine) and lag screws and washers to attach it to the post. All of the wood is pressure treated and the hardware is galvanized.

* Mailbox (USPS approved)
* (Qty 1) 8-foot 4×4
* (Qty 1) 6-foot 4×4
* (Qty 2) 5/16” x 3” lag screws
* (Qty 2) 5/16” x 3-1/2” lag screws
* (Qty 4) 5/16” flat washers
* (Qty 4) 5/16” split lock washers
* 2 bags of concrete. You may or may not need it all, but have two bags on hand. (I used approx. 80 lbs.)
* Quart of exterior grade paint

If your new mailbox needs a platform, add 2-3 more sets of 5/16” x 3” lag screws w/ flat washers and split lock washers. I used 3 on mine.

Getting Started On How to Build a Mailbox Post – A First Class Project

Make your own wooden mailbox post
The first 24 inches of this post will be buried in the ground and anchored with concrete.

Start with the main, vertical post. Grab the 8-foot 4×4 and mark a line 24” from one end (the bottom). This “ground line” shows you how deep to bury the post. The horizontal support arm mates to the main post with a half lap joint. The next step is to position that joint.

Half lap joint layout
Layout for one side of the half lap joint. It’s the width of a 4×4 (approx. 3-1/2”) and half as deep.

According to USPS guidelines, the bottom of the mailbox should be between 41” and 45” higher than the surface of the road. The road; not the ground the post is buried in. If your yard is higher or lower than the road, adjust accordingly. Either way, the first 24” of the post should be buried. Then add the mailbox height to that.

In my case, I measured 41” above my “ground line” (65” from the bottom of the post). This is where the top of the half lap joint – hence the top of the horizontal support arm – will be. After I add my mailbox support platform, the inside bottom of the mailbox will be about 42-1/2” inches higher than the road.

Part And Parcel – The Half Lap Joint

Curbside mailbox post construction
Every cut in this project was made with a circular saw. Set the blade depth to cut half way through the material.

The half lap joint is just a pair of dadoes that fit into each other. You can hog away the waste material with your circular saw. But there’s an easier, usually faster, way.

Cutting a dado with a circular saw.
First cut at the inside of both lines.

SAFETY NOTE: You can’t see in most of the pictures, but the wood is always clamped at two points (to one or both tables) so it can’t move while I’m making my cuts. Failure to secure the workpiece can lead to injury. Injuries bad, mmmkay?

Preparing to remove the waste material.
Make a series of cuts in between. They don’t have to be evenly spaced, or even parallel to each other.

Rather than trying to remove all of the material with your saw, make a bunch of separate cuts, as shown. Then knock out the waste wood and clean up the bottom with a chisel.

Break away the waste wood.
Next, use a large slotted screwdriver to pop out the waste wood.
Cleaning up the bottom.
The bottom of the dado cleans up easily with a mallet and chisel.

Dado The Support Arm

Matching dadoes
Cut a matching dado on the support arm.

The horizontal mailbox support arm is cut from the 6-foot 4×4. Select the better of the two ends (you can trim a little off if you need to). Leave about 5” then lay out and cut the other side of the half lap joint.

Half lap joint.
Test fitting the half lap joint. You may notice the two pieces don’t sit perfectly flush with one another; it turns out one 4×4 was slightly thicker than the other. But it’s close enough for tangential government work.

Mail Revue – Hunk It Up With A Decorative Touch

Easy accents for your mailbox post.
Some basic cuts add a decorative touch to the top of the post.

This mailbox post is based on a classic design. And true to tradition, we’re dressing it up with simple design elements: a pyramid at the top and an accent cut below that.

Locating the decorative elements.
Stand the new mailbox on end, above the dado. If the mailbox is going to sit on a platform, leave space for that.

I used the new mailbox to gauge where I should lay out my decorative accents. There is an accent cut 1”-2” above the top of the mailbox. Then a pyramid “finial” about 4” above that. These are purely aesthetic and can be altered to taste.

Marking for a decorative cut.
An inch or two above the top of the mailbox, mark a line for the decorative cut. Wrap the line around all four sides of the 4×4.

Pyramid Scheme In A Mail Dominated Industry

The next two pictures serve to (hopefully) prevent any potential confusion concerning the angled marks you may notice in a bit. You do not need to draw them on yours.

Positioning the pyramid.
Here, I was figuring out how much space was needed for the decorative pyramid accent.

I’ve already done the “figuring out”, so you can skip the whole triangle layout part. Just mark off a blank inch of material. That inch will become the ornamental pyramid.

Pyramid scheme.
Seriously though; skip this layout. Just leave an inch and you’ll be fine.

Trim The Main Mailbox Post And Support Arm To Length

Cut in two passes.
A regular circular saw can’t cut all the way through a 4×4 in one pass. No problem; make one pass that’s slightly deeper than halfway. Then turn the wood over to finish the cut.

Determine how long the mailbox side of the support arm needs to be for your particular mailbox, then trim it – and the main post – to length. The bottom edge of some mailbox doors (like my new one) tuck underneath the body when opened. Make sure the support arm won’t hinder movement of the door.

Alpha Mail – Cutting Decorative Elements Into Your Mailbox Post

Making the decorative cut.
Set the blade depth to 1/4” and make the decorative cut all the way around the post.

You can certainly get by without these cosmetic touches. But for the little extra time they take, they make a big difference in appearance. And if you want to tweak them to better suit your taste, do it! This is your how to make a mailbox post project too.

A decorative cut, 1/4" deep.
This saw has a thin kerf blade, so I made the cut about two to three passes wide.

To cut the pyramids that adorn the ends of the post members, angle the sole plate of your circular saw to 30°. Cut along a reference line drawn an inch from the end of the post, on all four sides.

Cutting the pyramid at a 30° angle.
Set your saw to 30°.
First side of the ornamental pyramid.
Here’s the first cut. Now rotate the workpiece and make the next cut.
The first two cuts.
The first two cuts. We’re halfway there.
Pyramid "finial".
With all four cuts done, you have a cool pyramid-like shape even your mummy can appreciate.

Pushing The Envelope – A Small Variation For The Mailbox Support Arm

Support arm partial pyramid.
On the long end of the support arm, I left the top side (where the mailbox will rest) uncut.

Admittedly, there isn’t a lot of “envelope pushing” going on here. But I’ve complied a list of mailbox puns and, since most of them won’t work for this project article, I need to use what I can when I can. ‘Cause frankly, I’m not finding much opportunity for contrived references to my “package” or pop singer “Post Mailone”. But when a sassy pun wants to heard, one must letter speak!

Cutting the last pyramid.
The short end of the support arm gets the full pyramid treatment.

Mail Bonding – Joining The Two Main Parts

Partial post.
Main post and support arm. (Top view)

The parts fasten together with lag screws. But first, we need to drill holes for each screw location. Start by drilling counter-sinks into the support arm.

Galvanized hardware.
5/16” x 3” galvanized lag screw with a split lock washer and flat washer.

Use a Forstner bit (or paddle bit) to make two holes large enough for the flat washers and deep enough to just sink the heads of the screws.

I drilled two 7/8” holes, located diagonally on the lap joint. Space them apart, but not too close to the edge. (Despite that gap at the one corner, this is a solid, tight-fitting joint.)
Deep enough.
The holes should be deep enough to just bury the hardware, as shown. It will sink below the surface when tightened.

After drilling the counter-sink, drill a pilot hole. A pilot hole prevents splitting by giving the shank of the screw somewhere to go.

Drilling pilot holes.
I used a 7/32” twist drill to make a pilot hole 3” deep (the length of the screw, not including the hex head). Conveniently, the bit that made the counter-sink holes also marks the center for you.

I made 7/32” pilot holes. But with harder wood, a 1/4” pilot is commonly recommended for 5/16” lags. For best results, test on a piece of scrap to determine what works best with the wood you’re using. Finally, separate the two pieces and enlarge the holes in the support arm (the piece with the counter-sinks) to 5/16”.

Finally, counter bore.
Drill 5/16” counter-bores all the way through the support arm only, enlarging the holes that were already there. During assembly, the lag screws should pass easily through the support arm holes and thread into the main post.

Mail Support Group – Brace Yourself (And Your Mailbox)

Diagonal brace.
The long side of my brace is 15”.

The diagonal brace is cut with a 45° angle on each end. The brace is attached with two 3-1/2” lag screws.

45° arm brace.
Drill counter-sinks, pilot holes and counter-bores, the same way you did before.
Perpendicular to the face, not the angle.
When drilling for the lag screws, stay perpendicular to the face of the support brace. Ignore the angles.
Brace in place!
Brace in place!

The Post With The Most – Prep And Paint That Mofo

Prepping for paint.
Here, I’m cleaning the surface with a wire brush (stroking mostly along the grain) to remove dirt, debris and any loose fibers to prepare for painting.

Now that you’ve successfully built your mailbox post, take it back apart! Sand or wire brush all of the wooden parts then give them a couple coats of exterior grade paint. I chose a green that matches the shutters on the home. Let it dry overnight before installation.

Mailbox platform.
If your new mailbox is going to sit on a platform, have it cut and ready as well. This platform leaves room at the front for the door to open unobstructed.

Post Mental Pause

Out with the old mailbox and post.
Ousting the old mailbox was simple: I pulled a handful of screws then lifted it off of the post. Uprooting the old 4×4 was easy too. It was just barely in the ground.

Rock the old post back and forth until it’s loose enough to lift out. It may take some extra persuasion and you may have to dig a bit if it’s anchored in concrete. In this case, however, not only was it not anchored, it was only buried 10” deep. Geesh, how was this thing even standing?

Going Postal – How to Install a Mailbox Post

Digging two feet deep.
Dig a 24” deep hole for the new post.

If you’re installing a mailbox at a fresh location, you should first have the area checked for any underground utilities.

According to Post Office guidelines, the front of the mailbox should be set back 6-8” from the edge of the road. This required my moving the existing hole back several inches. And of course, to deepen it to 2 feet. The 4×4 post should be able to sit in the hole with 3-4” of clearance all the way around.

Temporary bracing.
Clamp on some temporary braces to hold and steady the post while you work on the concrete. Check multiple times throughout the process that the post is plumb in both directions. You don’t want to set a crooked mailbox post.

Tamp the bottom of the hole a few times, verify that it’s right at 2 feet deep, then insert the post. Be sure the front is turned parallel to the road. For visual reference, you can hold a yard stick against one side of the post and extend it towards the road. This “pointer” helps to judge if the post is properly squared up to the road.

Keep Me Posted – In Concrete

Concrete; the layering method.
You may prefer to mix your concrete, then pour. I went with the layering approach. That way, I only used as much concrete as was needed. And there was virtually no cleanup afterwards.

Assuming you followed the Postal Service guidelines (front of mailbox 6″-8″ from the road and the bottom of the mailbox 41″-45″ higher than the road) – and oriented the post properly (double check to be sure you have the correct side facing the road) – you’re ready to set it and forget it.

Leave 4" for dirt on top.
After mixing in what I can of this last bit of water, I topped the hole off with dirt.

Rather than mix the concrete first, you can pour in several inches of dry concrete then splash in enough water to completely wet what’s there; it will probably take less than you think. Poke, prod and mix until you see no more dry powder (I used a piece of rebar as a stir stick). Then add a little more concrete, water, mix, lather, rinse, repeat. Remember to check for plumb a few times during this process.

Curbside mailbox post assembly.
Bolt the support arm in place, followed by the diagonal brace.

Continue filling the hole until you’re about 4” from the top. When the surface of the concrete hardens (maybe an hour or so), top it off with dirt. Finally, remove the bracing and assemble the mailbox post. It can take six hours or more for concrete to truly set (and several days to fully cure), so don’t be too rough during assembly.

Mailbox platform in place.
If you’re using a mailbox mounting platform, drill and attach it just like the other parts. Fasten with 3” lag screws and washers.

Mail Call!

Touch-up paint.
Complete the look by touching up all the exposed hardware with matching paint.

All that’s left to do is paint the exposed hardware and screw the mailbox into place. This new mailbox will save me a ton of time and gas money. And my “mail escort” won’t have to leave as many packages out in the rain.

New mailbox and post: reporting for duty!
A fresh new mailbox, ready to send treasures and receive bills. It’s a one-way relationship, but I kind of feel like I’m the winner here.

I always feared: What if there’s not enough room for the endless piles of “last chances” to win some clearing house’s sweepstakes? Or all of those fake keys the car dealerships send out, coupled with promises of either a big screen TV or a coupon for $5 off of a new car: just for showing up! But I shall worry no more; this mail beast has room for all of that junk mail and so, so much more!

Belly of the beast.
This gaping maw dwarfs the old mailbox. For reference, the narrow box on the right is 12-1/2” tall.

The extra large capacity mailbox we used can be purchased for under $27.00. This one is black, but other colors are available as well.

Buy Now - via The Home Depot

Call before you dig:

More Info - via

USPS mailbox guidelines:

More Info - via

More information regarding official requirements for city delivery mail receptacles:

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About Steve

Steve made his first woodworking project at age 9 (in 1982) and whittled his first wooden chain at 18. He was also a consumer electronics repair tech and shop owner for a little over 20 years, until his impending obsolescence became impossible to ignore. Since then, Steve has focused passionately on manipulating his wood... in his workshop. Don't judge him.

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1 thought on “How To Make And Install a Curbside Mailbox Post”

  1. Actually, the pyramid cut at the top of the vertical post isn’t only cosmetic. If you cut the tip off the post horizontal and you install the post vertically plumb, the top of the post will allow water to pool there. This will cause even treated wood to rot much more quickly.


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