Norma relacionada
Mexico
Practice Relating to Rule 125. Correspondence of Persons Deprived of Their Liberty
Mexico’s Army and Air Force Manual (2009), in a section on the 1949 Geneva Convention III, states: “Prisoners of war are allowed to send and receive letters and cards free of postage.” 
Mexico, Manual de Derecho Internacional Humanitario para el Ejército y la Fuerza Área Mexicanos, Ministry of National Defence, June 2009, § 167(E).
In a section entitled “Basic rules of international humanitarian law applicable in armed conflicts”, the manual also states: “Captured combatants and civilians under the authority of an adverse party … have the right to correspond with their families”. 
Mexico, Manual de Derecho Internacional Humanitario para el Ejército y la Fuerza Área Mexicanos, Ministry of National Defence, June 2009, § 409.