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Not for physical mail.

Yeeeeey for living in a country where physical mail is prohibitively expensive. A standard letter, 2 - 5 business days, costs $3.50.

In US, USPS (government snail mail) literally has program that allows you to send^W spam marketing mail: https://www.usps.com/business/every-door-direct-mail.htm

Do they make it up on volume or is postal workers just incredibly cheap?

They're forced to deliver it at a loss and then yelled at by congress when they fail to turn a profit. The system just works.