La Poste postage stamps are valid for use in the Overseas Departments, but not in the Territorial Collectivities, which issue their own stamps, separate from metropolitan France.
It also operates postal services in Monaco and Andorra.
In addition to postal services, it also offers banking services and, via Chronopost, courier services.
Encyclopedia De LaPoste Maritime Francaise by Raymond Salles The entire world of French Maritime mail including the U.S., Nine volumes, 1,933 pages, 2,800 markings, 20,000 voyages, 122 maps, in French.
Combination Mail of British Post Offices Abroad, An Introductory Survey by Geoff Kellow A beautiful little study, we hope the words An Introductory Survey means a larger work will be forthcoming.
The British Sea Post Offices in the East, British Maritime Postal History by Hector Proud, Though this is vol 4 of the series it stands by itself as to covering the subject.