Corona version 9
The model uses materials that may not be displayed correctly in very old versions of the engine.

A set of three types of mailboxes from Safety letter box:

Tile – https://www.safetyletterbox.com/in-front-out-front-horizontal/the-tile-mailbox 
Moda – https://www.safetyletterbox.com/moda-system-mailboxes/moda-horizontal-s-mailbox 
Moda close – https://www.safetyletterbox.com/moda-system-mailboxes/moda-horizontal-300-mailbox 

Each type of boxes is grouped into 40 pieces and made in 2 materials.
The archive contains textures with numbers from 001 to 120 and from 101 to 500.
You can always add more variation with these textures.

Objects are partially attached textures and materials have logical names
Texturing UnwrapUVW

For Corona render it is recommended to install a version not lower than 1.5 since the glossiness of materials is configured with PBR in mind.

Who works in a V-Ray version lower than 3.1 be careful in the materials in the BRDF section there is a Microfaset GTR ( GGX) if your version is older than 3.1 then the BRDF field will be empty. Choose Blinn Phong or Ward – which is preferable for you