.. Find the stamp's city

Look at the stamp in the evidence tab. Read what it says on the stamp.

Can you date the stamp?

"Andrinople" is a hint. That city is not always called that.

Here's the wikipedia page for Edrine, former Andrinople.

Edrine was called Andinople until 1923.

What language is the stamp written, by the way? The text reads "POSTES OTTOMANES".

Use google translate and let it detect the language of "POSTES OTTOMANES". ( It is French. )

The city name in the cancellation mark must be written in the same language: French.

So, you are looking for a city that existed before 1923 and which french name contains "ROUT".

It is a capital of a nearby country.

In French: Beyrouth ( Type in: BEIRUT )