In amateur radio, it is usual after each QSO,if desired to send a QSL card.
The confirmation cards are a successful wireless connection (QSO)
Here you can see some of my oldest QSL cards.
Europe
Transoceanic
My QSL card info:
directly by www.e-qsl.com
via bureau about our
German Amateur Radio Club DARC, Lindenallee4, 34225 Baunatal Germany
For all, who send me a QSL card via www.e-qsl.com, I ask for another paper QSL card via bureau or direct, for my collection.
If it is possible. Thank you!