When I mail a letter to Kenya, I pay in US postage. The US ships it to Kenya, drops it off at their postal service and then the Kenyans deliver it throughout their country. Is it just good practice for them to deliver all incoming mail, even though they may not profit from it?
One reason I can think of is that they rely on the fact that the receiver will probably mail back through their own postage currency?
But are there any other costs involved in paying for the in-house delivery? Perhaps an extra cost included in the postage?
That’s essentially it. The argument was that letters usually get a reply, so you’d make it back then (the cost is factored into the cost of international postage rates in each country). Eventually, all countries agreed to abide by the policy.
There have been some issues about some countries being net exporters of mail, while others are net importers, thus causing inequalities. The problem has been raised, but no solutions have been approved.
One country for which this is very true is the Cayman Islands. When I was there (circa 1999) mailing a postcard to the US cost 25 cents (about 30 cets US). They took all US bound mail and sent it via plane to Miami. The US Postal service had to sort it and do a much larger fraction of the actual delivery.