USPS ships about 40 percent of Amazon’s packages. Amazon bulk-delivers packages to a USPS distribution center, and the Postal Service brings it to your door. USPS negotiates the discounted rate for that service with Amazon, as it does all other bulk shippers.

In 2017, parcels brought in $19.5 billion, or 28 percent of USPS’ annual revenue. At $2.1 billion, packages contributed the largest revenue increase.

Deals with private shippers like Amazon accounted for $7 billion of the $19.5 billion in revenue. While we know that Amazon is the biggest e-commerce player, we don’t know exactly how much of the $7 billion comes from Amazon, because the details of the postal service’s deals with private shippers are considered proprietary and not made public.