I am planning to install posts and attach a mailbox as shown in the picture. There are a couple of unknowns and I would like to benefit from the knowledge of this community before I begin this project.
1. I would be using 125mm x 75mm posts. Which type of wood should I use? Cypress or hardwood? Does it need to be treated?
2. What stain should I use to make it look like in the picture.
3. How deep the posts should be concreted keeping in mind that they are not load bearing?
Thanks for sharing your question about the type of post to be used for your mailbox. Cypress is very suitable for in ground use. It's naturally rot and termite resistant. H4 treated timber can also be used in direct contact with the soil. Any timber you decide to use must be rated for in ground use.
In regards to the colour, I suggest going to the decking oil sample board in the paint department so that you can see the different finishes. This will give you a better idea of the kind of colour you'll be getting. Looking at the photo you posted, it looks very much like the same colour as the Merbau decking board steps.
Since the post is not load bearing, I propose a depth of 300mm and a width of 200mm so that there will be enough space for the concrete.
If you need further assistance, please let us know.