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!

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.


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!