> USPS is extra weird, because the recipient pays (via ad exposure) for the benefit of the sender (low postage).
No this is 100% wrong.
We do not subsidize bulk mail, the rates we pay are a penalty for the difficulty of processing our mail.
Bulk senders only receive preferred rates if they conform to very specific specifications about presorting, proper labeling, where the mail is dropped off, how far it's traveling, quantity, size, and weight. All of these factors and more impact the cost of the USPS to process a single piece of mail. The business doing some of that preprocessing saves the USPS money and they pass the savings on to the business.
USPS offers flat rate, media mail, and priority options that have dimensional and weight restrictions because those allow them to more cheaply and efficiently process those packages.
