In "The Worst Crime in the World" by G. K. Chesterton, Sir John was talking about his son who just left the country:
“Some people I never heard of, called Grunov, have been pestering me, of all people, about his whereabouts,” said Sir John; “and I’ve just come in to send off a wire to tell them that, so far as I know, he’s living in the Poste Restante, Riga. Even that has been a nuisance. I came in yesterday to do it, but was five minutes too late for the post office. Are you staying long? I hope you will pay me another visit.”
How can someone live in a Poste Restante? Or he just meant live in somewhere close to the Poste Restante?
And why was this phrase written with Capital letters?