There are so many different types of columns you can build to hold a mailbox, and so many types of materials available, that it is hard for me to give very specific advice on the building of the column. However, I can give you some basic tips on how to mount our mailboxes in any column.
1. Mailboxes are not designed to become part of the structure of the column.
We have built a Fast-Trak Mounting plate into several of our curbside models which allows you to mount the mailbox in the column and remove it anytime for cleaning or any other maintenance. It is just not a good idea to mount a metal mailbox into a stone or cement column with all sides touching this wet and porous material even if the box is extremely rust resistant like ours. Not only will you scratch the finish but there are chemical reactions that could take place and prematurely cause rust. If the mailbox is part of the structure you are left with few if any options.
2. Make sure there is a base inside the column.
Whether it be wood or some type of brick or stone, use a structure on the base of your column where you can mount the Mounting Plate easily without having to work from within the confines of the box. There are plenty of different hole patterns on the mounting plate, so it will attach to just about anything with the correct hardware.
3. Make sure you are within USPS regulations.
Please contact your local Post Office before you build a mailbox column to make sure you are following local rules and guidelines for a locking mailbox.