During the latter quarter of the 19th century, commercial correspondents often saved postal cards because the sender's message was written on the card, whereas they tended to discard envelopes saving only the contents of the envelope. Thus, we are fortunate as postal stationery collectors to be able to acquire postal cards from diverse, unusual origins.
Here's an old Peruvian 4-quatro postal card sent from Callao, Peru's premier Atlantic ocean port, January 15, 1887, received on February 22, 1887, in Luxembourg ,with Luxembourg-Gare and Luxembourg-Ville receiving cancels.
It's quite a treasure as pre-1900 mail from Peru to Luxembourg is very scarce. Happily, this commercially used postal card was saved!