Odessa  :

The letter was accepted at the Odessa General Post Office, prepaid with 13 kopecks (stamps of 10 and 3 kopecks), and marked with the "P.D." stamp (*Payé jusqu'à destination* / "Paid to destination").

The postage totaled 13 kopecks (using 10-kopeck and 3-kopeck stamps from the second issue of 1866–1870), which exactly matched the Russian Empire's international rate for sending a letter weighing one *lot* (approx. 12.8g) to France via an overland route.

Warsaw (Back, top right — MAY 12):

The letter arrived in Warsaw by train from Odessa. On May 12, 1875, it underwent international sorting at the Warsaw Foreign Mail Processing Office (marked "WARSAW * FOREIGN MAIL PROCESSING").

Railway Post Office Car No. 21 (Back, top left — MAY 29 / May 17 Old Style):

The letter was loaded onto Railway Post Office Car No. 21, traveling the Warsaw ➔ Aleksandrowo (Prussian border) line. A cancellation mark bearing the New Style date (May 29) was applied at the car's post office.

Transit via Prussia and Belgium (Front):

From Aleksandrowo, the letter was transferred to a Prussian railway post car (Thorn ➔ Berlin ➔ Cologne) and then transited through Belgium to the border station of Erquelinnes.

France / Erquelinnes – Paris (Front, right):

At the Belgian border station, the French railway post service applied a blue "RUSSIE / ERQUELINNES - PARIS" handstamp. Marseille (Reverse, bottom right — 27–28 MAI):

The letter passes through Paris, arrives in Marseille (southern France) on May 27, and is delivered to the addressee on May 28, 1875.

The presence of an identifiable postmark from Railway Post Office Car No. 21 (Warsaw-Alexandria Railway) transforms this item from a simple piece of international mail into ideal documentary evidence of the operations of the Russian Empire’s Northwestern export postal route during the 1870s!