Postal services in Andorra are unique in that they are not operated by the country itself, but by its two larger neighbouring countries, Spain and France.Andorra , Universal Postal Union, September 2004 This is a legacy of the centuries of de facto control exercised by those two countries over Andorra. Correos of Spain and La Poste of France operate side-by-side. However, the postal code system, introduced in July 2004,Muhamad Amin, Sara and Wilson, David (2014) Designing a Postcode System for Arbil City, Iraq., International Journal of Computer and Communication Engineering, V3 (5) page 381. ISSN 2010-3743 has a different format from those of either Spain or France, consisting of the letters "AD", followed by three digits.
Both postal administrations issue their own postage stamps for use in Andorra featuring unique designs,Andorra honors Pinoys with a stamp, Daniel Infante Tuaño, ABS-CBN, July 18, 2014 as those of Spain and France are not valid.Spain, Damien Simonis, Lonely Planet, 2007, page 412 These are used for international correspondence, as postal service within Andorra is free.Europe Review 2003/04: The Economic and Business Report, Kogan Page Publishers, 2003, page 12
References
fr:Histoire philatélique et postale de l'Andorre#Fonctionnement depuis 1931