I just received a letter from a friend of mine in France, and it occurred to me that he had purchased his stamps there in France. Why then did the U.S. Postal Service bother to deliver the letter? What’s in it for them? How does this intercountry mailing business work, anyhow? –Ray Balestri, Dallas

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First the easy part. Cheap, efficient international mail was one of the great achievements of the Victorian era. Previously, trying to get a letter delivered overseas had been an accounting nightmare. In calculating postage, hapless users had to figure in the local rate in their home country, the rate paid for ship transport (“sea postage”), the rate paid to each country that handled the letter en route (“transit fees”), and finally the domestic postage in the destination country.

Fed up with this, the U.S. called for an international postal congress, which was held in 1863. This led to the creation of the Universal Postal Union, 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 short, the international mail system is beginning to approach the complexity it had prior to 1862, with two UPU formulas, a European formula, and a Canadian formula. We still pay transit fees, too. Happily, consumers haven’t been affected much–so far. Though its own accounting is getting knottier by the year, the U.S Postal Service inflicts only three international rates on users–one for Canada, one for Mexico, and one for everybody else. But we could yet wind up with separate rates for every foreign destination.