What are the recommended dimensions for a mailbox post?   

The post size recommended is a 4x4. The post should be submerged 2 feet into the ground and stick up either 2 feet above the ground or 3 feet above ground depending on the model of your Step2 mailbox. Refer to you Step2 instruction sheet for the model you have purchased and additional directions. Please contact the US Postal Service for required distance from the road.