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

Once upon a time there was an elegantly simple answer to this question. Not today. After 20 years of well-intended tinkering, international mail has overtaken Christmas-toy-assembling on the complexity index, and it’s breathing down the neck of VCR-clock-setting. So brace yourself.

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.

Postage could vary widely depending on the route by which you sent a letter–from five cents to $1.02 per half ounce from the U.S. to Australia, for instance. Detailed accounts had to be kept for each mail shipment so that everybody who got his mitts on it in transit would be sure to get his proper share. We had separate postal treaties with every country, and everybody figured things differently–by the ounce, by the gram, by the German “loth,” by the sheet. Predictably, the mail was slow and the rates were exorbitant.

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.

The rationale for item number three was ingenious. Reformers argued that each letter begot a reply. If each country had as much outgoing mail as incoming, the international postage it took in would cover the cost of delivering foreign mail.

The new system worked fine for quite a while. Postal rates dropped, international mail boomed, prosperity reigned. But by and by grumbling arose, partly because the nature of the mails had changed. One-way commercial mail such as periodicals came to account for a much larger portion of mail volume than letters. Countries like the U.S. became net exporters of mail. Since we kept the postage, poor nations griped that they had to deliver our mail essentially for free.

So in 1969 the UPU decided on a new system. If we sent India 100,000 kilograms of mail per year and they sent us 80,000, we’d pay them a fee for the 20,000-kilogram difference. These fees were called terminal dues.

That opened the door to a long round of rate tweaking. Since terminal dues were originally charged strictly by weight, bulky periodicals incurred huge costs while letters, which required just as much handling, got off dirt cheap. Complaints from the U.S. and other nations finally prompted the UPU to devise a new “threshold” system, to be implemented in 1991. It sets separate letter and periodical rates for countries we send at least 150 tons of mail to annually. For countries we send less mail to, the old flat rate is kept. Meanwhile, we negotiated a separate terminal dues formula with 11 European countries that includes a rate per piece plus a rate per kilogram. We have yet another arrangement with Canada.

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.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.