The United States Postal Service delivers millions of pieces of mail every day to homes and businesses around the country. If you live in an area that includes roadside mail delivery by a rural carrier, however, you will need a mailbox installed correctly according to the USPS regulations to receive mail. Whether you want to install a new mailbox or replace a broken one, you will need to put in a post to mount your mailbox.
Contact all of your local utility companies prior to digging, if you are placing the mailbox in a different location than a previous one. Verify this location with your local USPS postmaster or mail delivery person also, if this is not replacing a box in the same location. You must install the mailbox at a location approved by the USPS.
Dig a hole three times wider than the mailbox post's dimension and around one-third of the length. A typical 5-foot mailbox post requires a hole 15 to 19 inches deep and 7 inches wide. Adjust these amounts if the post's instructions differ. The USPS policy for curbside mailboxes requires the height at the bottom of the mailbox to be between 41 to 45 inches and the front of the mailbox at 6 to 8 inches back from the road or curb, unless your specific postmaster states otherwise.
Add 6 inches of gravel into the hole for drainage. Put the post in the middle of the hole and verify the height at the bottom of the mailbox meets the 41- to 45-inch USPS standard. Add or remove gravel to adjust the height. Have someone help you hold the post or do the measuring, if possible. You can temporarily brace the mailbox using wood and clamps to complete the installation yourself.
Place a post level on the post and adjust as needed until level. Fill the hole with the quick-dry concrete leaving a 4-inch gap at the top of the hole. Verify the post is level again, and then add water as directed to the concrete.
Wait at least 30 minutes for the concrete to set. Add dirt to the hole up to ground level and then firm it.
Install the mailbox on top of the post according to the directions supplied. This usually requires screwing the mailbox to the horizontal bar or post extending out from the post.