How to Lengthen a Mail Boss Mailbox Post

For mailbox post installations more than 1′ in the ground

So you want to use an In-Ground Post for your mailbox installation, but one foot in the ground just isn’t going to be enough? Sometimes you just need a little more length, and we will cover some things to consider:

First, a little general information about curbside mailbox installations

The most common application for a mailbox installation is on an In-Ground Post. The In-Ground Posts we offer are 43″ in length, which allows you to install them 12″ in the ground, leaving 31″ above the ground above the road surface.

Many people wonder how this allows you to have your mailbox 41″ – 45″ above the road surface, which is required by the United States Postal Service. The key is that for locking mailboxes the USPS wants the incoming mail slot or bin (as opposed to the bottom of the mailbox) 41″ – 45″ above the road surface. The incoming mail slot/bin on the Mail Manager, Mail Boss and Package Master are 11″ – 13″ above the floor of the mailbox, so installing these mailboxes on an In-Ground Post buried 12″ in the ground places the incoming mail slot/bin 42″ – 44″ above the road surface.

But what about if you need to go deeper than 12″ in ground?

Perhaps you have a deep frost line, or a very heavy installation, so you need more than 12″ in ground for additional stability. No problem!

mailbox posts for outside deep ground post mounted mailboxes mailbox post cover Modern Architectural Epoch Design

The bottom of the In-Ground Post has four predrilled holes in it, so you can easily secure a treated 4″ x 4″ wooden post inside of the In-Ground Post to add additional length. If you would like to go 24″ into the ground, place the treated wooden post inside of the steel post leaving 12″ sticking out, and bolt the wooden post to the inside. This allows you to still leave the necessary height of the steel post above the road surface to meet USPS specifications.

And what if you need more than 31″ of post above ground?

Maybe you have an unusual application. Perhaps the ground surface where you are installing your post is actually below the road surface, or your postal carrier has requested your incoming mail slot/bin be above the standard 41″ – 45″. Not a problem. In this case you will definitely want to use a treated wooden 4″ x 4″ post inside of the metal post. You can bury as little as 3″ – 6″ of the metal post in the ground, with the rest of the In-Ground post length provided by the wooden insert. You can play around with the length as necessary.

New for 2023, we are proud to offer our Mail Boss Post Height Extension, and Post Depth Extension Which allow you to quickly and easily extend the height and/or depth of your Mail Boss brand steel mailbox post. The Mail Boss Post Height Extension will raise the height of your post six inches once installed. The Mail Boss Post Height Extension is color matched to your existing post and easily installs with the included hardware. The top mounting pattern fits all Mail Boss brand locking security curbside mailboxes. Ideal for landscape changes or issues where the mailbox is mounted too low to the ground.

The Mail Boss Post Depth Extension is perfect for increasing the length of any Mail Boss steel mailbox post. The Extender is bolted inside the post at variable heights, and holes are pre-drilled at set distances of 3″ apart, allowing for a variety of installation heights. Optionally, at the bottom of the post depth extension there are 4 sets of aligned cross holes, which conveniently accommodate up to 4 sections of #4 rebar (1/2″ Diameter). Avoid measurements, save time, and shore up your install with the MailBoss Post Depth Extension.

Hopefully, we have covered most typical questions with regard to unusual post installations. If not, please don’t hesitate to contact us with additional inquiries!


  1. Brent on September 20, 2015 at 10:07 pm

    Hello. Last week, I replaced my driveway and sidewalk. We also removed the old mailbox, and since we loved the construction of your product compared to everything else, we agreed to get the mail manager. We couldn’t get the mailbox until just today, but was able to purchase and cement in your steel post last week before we had the box. I was unaware of the 41-45 inch height, and now it seems I may come up a little short for the height. I just read your info concerning extending the height, but it’s too late to insert a 4×4 into the post because it’s already cemented in. Do you have any suggestions? ….. Just a suggestion of mine: I think if Mailboss was to create different height heavy gauge steel “shims” with appropriate longer screws for mounting under the box, maybe in one inch increments?…I think that would be a useful product to add to your line. I’d be buying one now if you offered something like this. Thanks for reading, and thanks for any response or suggestions you may have with possibly correcting my dilemma. Brent

  2. Jenny on October 1, 2015 at 1:18 am

    Hi Brent,

    Sorry for the delayed response. Hopefully you contacted us directly and someone was ale to help you. You should be okay with the Mail Manager and a 43″ in ground post buried 12″ in the ground, as the USPS specs are different for locked vs unlocked mailboxes. The height is 41-45″ from the road surface to the INCOMING MAIL SLOT on a locking mailbox (vs the floor of an unlocked mailbox). Hope this helps!

    Mail Boss

  3. Brent on October 6, 2015 at 12:29 am

    Thank you for responding Jenny… I did not contact Mailboss directly, instead I contacted you via my last email. My actual problem is this: The hole I dug for the post is much deeper than 12 inches (my concrete guy told me to dig deeper for the post)… Because I was unaware of the heights that is required by the postal service incoming mail slot, it ended up that after we cemented in your 43 inch post, and got the Mail Manager mounted, the incoming mail slot measures about 38 inches above street level… This is my dilemma.. The post is maybe 2 inches cemented in too deep to facilitate the usps spec requirements. This is why I was suggesting in my previous email that if Mailboss were to create “heavy gauge steel shims” in 1 inch increments that can be mounted (with appropriate lenght bolts) UNDER the mail manager and ON TOP of your post. I would buy a 1 or 2 inch shim from you to solve my issue… Luckily we have a cool mailman who says it’s okay being as low as it is, but I would like to make it up to usps specs anyway…. Thanks… Brent…Understand?..

  4. Jenny on October 6, 2015 at 5:30 pm

    We emailed you directly regarding your inquiry.

  5. Carrie McCann on October 25, 2015 at 5:44 pm

    Before worrying so much about USPS’ required heights, check your local PO to see if they care! Our carrier and PO only care need their opening to be accessible w/o bending much, or being hard for a shorter mail-carrier to reach. They’re not robotic about exact height.
    But “Your mail carrier may vary.” So pls ask.

  6. Jenny on October 26, 2015 at 7:02 pm

    This is true! Good advice.

  7. Ned on September 2, 2016 at 10:24 pm

    I have the same problem. I buried my post to deep. How did you resolve the provlem i am looking for a spcacer. Thnks

  8. Mail Boss on September 6, 2016 at 11:23 am

    We don’t sell any spacers. The 43″ post should be within specifications if buried 12″ in the ground.

  9. Bruce on December 21, 2016 at 3:17 pm

    Is it ok to bury 43 inch post less than the recommended 12 inches to achieve more height of mailbox?

  10. Mail Boss on January 3, 2017 at 11:20 pm

    Yes, but you may want to consider reinforcing with rebar stakes!

  11. Linda Loushine on October 15, 2017 at 10:55 am

    I need to lengthen the height of my post, however, my custom made post is round. Any ideas? Thanks!

  12. Thomas Linton on June 29, 2018 at 5:12 pm

    RE roadside rural mailbox. Not knowing better, I bought at Home Despot, and I bought the hollow, square cross-section aluminum pole that they said went with the mailbox. BUT even with only 11″ in the ground, the box floor is only 35″ above the pavement – 9″ less than USPS suggests and 6″ less than USPS requires as a minimum. Furthermore, the square pole is smaller inside than a 4×4. I suppose I can try to trim down a 4×4 to insert to extend the inadequate pole. Easier fix? Thanx. Tom in Ohio.

  13. Gabriel on July 10, 2018 at 12:41 pm

    Hi Thomas, thanks for your inquiry. Locking mailboxes call for the point of mail entry to be 41″-45″ above the level of the road surface. Regulations ask for this so that the mail carrier can easily drive up and delivery your mail without getting out of their vehicle. Make sure that the mail entry is 41-45″ above the road surface (often times the base of the mail box is lower than the point of mail entry by about 8-10″. Thank you!

  14. Brenda harkins on June 9, 2020 at 8:56 am

    I have a mail box pole cemented into the ground , But it’s Not tall enough . How can I add length to it ??? Thank you

    • Gabriel w/ MailBoss on June 12, 2020 at 10:08 am

      Hi Brenda, thanks for your comment. What kind of pole is it? If you could send us a picture of your installation to we may be able to look at it and offer some advice.

  15. John Tindell on September 21, 2020 at 6:55 am

    is the OZ Post T4 600 4” 24” long metal drive in ground suitable for mail boxes?

    • Gabriel w/ MailBoss on September 30, 2020 at 10:13 am

      Hi John, thanks for your comment. We have not done an install with that product before, so I’m unsure if our post will fit over the top of it with the 4×4 as well, however you could always use the 4×4 above it, and then sink both that drive in and the wooden post, with our mounting post attached above it into the ground. We always recommend using a bit of fast-setting concrete to help solidify the install, especially if you want it to last. Our curbside boxes weight in between 20-53 lbs, depending on the model. Regards, and good luck!

  16. Morgan on February 20, 2021 at 4:34 pm

    What is the suggest length of the 4×4? Most hardware stores sell 4x4x6 or 4x4x8, so I need to have it cut. Would a 4x4x3 work?

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