Shipping items is taxing on the environment, but there are ways to reduce your impact on the environment when sending things to friends, family, and customers. Start by recycling a box. Most of us have boxes laying around. If it has printing or labels on it, flip it inside out and re-tape it. Write the address right on the package, there is no need to use a label. For delicate items, use newspaper as a cushion instead of styrofoam packing peanuts (it's much better for the environment). Encourage the recipient to recycle the box and packaging.
When you receive a package, make sure to recycle the box and all packaging materials. If your package included styrofoam packaging peanuts you can take them to a pack and ship store to be reused.
When taking a trip to the post office, consider walking or biking.