International postage recriprocation?

If I mail a letter from the US to Canada (for instance), I put my US postage stamp on it and it will be sent out to Canada. How does the postal service of the destined country (Canada) get paid?? Or do they?International postage recriprocation?
We have agreements with countries to balance the costs. It is very complicated and constantly changing.



The Universal Postal Union was created in 1863, which established a few straightforward principles: (1) there should be a more or less uniform flat rate to mail a letter anywhere in the world; (2) postal authorities should give equal treatment to foreign and domestic mail; and (3) each country should keep all the money it collected for international postage.



In 1969 terminal dues were established to pay countries where there was a big difference in weight in and out.



In 1991 the "threshold" system was established. It set separate letter and periodical rates for countries we sent at least 150 tons of mail to annually. For countries with less mail, the old flat rate was kept. Meanwhile, we negotiated a separate terminal dues formula with 13 European countries that included a rate per piece plus a rate per kilogram. We have yet another arrangement with Canada.International postage recriprocation?
The sending country gets the money, when you get an answer from Canada they get the money