Offering volume incentives is a common business practice in the U.S. and around the world. Although the U.S. Postal Service offers incentives to businesses that presort their mail, the agency does not offer incentives based strictly on the volume of packages shipped. One reason might be that offering volume incentives would lower the profit margin on each package shipped; yet, the potential volume increase of items shipped would make up for the smaller profit margins.
No pain no gain. The U.S. Postal Service has reduced spending over the past decade but it has come with a downside, notably a reduction in service. Over the past decade the Postal Service has reduced labor costs by $10 billion, improved productivity, and generally reined in spending.