Mailbox Stand and Planter - from www.archchemicals.com/Fed/
Every mailbox needs a stand to support it. This is such a stand. Detailed plans and pictures without instructions. Is in standard dimensions (ft and ins) also is in PDF file.
The first class letterbox - from Hands On
Here's a handy, highly saleable item that's not only attractive, but quick and easy to build, as well.
How to make a mailbox - from Buildeazy
This mailbox has an area for letters, newspapers and bottles. Is in both metric (mm) and imperial (ft and ins) dimensions.