When working overseas hams, particularly when they live in the third world it was common to mail them enough IRC's to cover the return postage for them. Now while QSL cards haven't disappeared most of it has moved to the web and digital confirmations.
Felt like a fun old-timey experience, like sending a telegram or postal order. Most of my relatives apparently couldn't work them out though, even though I included detailed instructions.
Additionally, my best man sent my father-in-law the traditional congratulatory telegram, which they "delivered" by calling him on the phone and reciting it, then mailing the physical telegram.
(apparently I'm old, at least that's what my son who was born in January 2000 keeps saying)
“ In 1920, Charles Ponzi made use of the idea that profit could be made by taking advantage of the differing postal rates in different countries to buy IRCs cheaply in one country and exchange them for stamps of a higher value in another country. His attempts to raise money for this venture became instead the fraudulent Ponzi scheme.[24] In practice, the overhead on buying and selling large numbers of the very low-value IRCs precluded any profitability. The selling price and exchange value in stamps in each country have been adjusted to some extent to remove some of the potential for profit, but ongoing fluctuations in currency value and exchange rates make it impossible to achieve this completely, as long as stamps represent a specific currency value, instead of acting as vouchers granting specific postal services, devoid of currency nomination.[25]”
There were said to be queues outside the offices of shops, bodega in NY for the community in question all day and all night.
e.g. Post Luxembourg sells them for 2.20€ with free international shipping: https://www.postphilately.lu/en-US/products/collectionneurs/...
France's La Poste sells them for slightly cheaper but has a fairly high minimum for free shipping (75€ if i remember correctly?): https://www.laposte.fr/pp/coupon-reponse-international-abidj...
