In 1878, the Mexican Post was invited to join the Universal Postal Union, joining said institution on 1 April 1879. Later, on 1 January 1884, the First Postal Code and Rules take effect, and in 1895 they are subsequently replaced by the second Postal Code.
In 1900, the national territory is divided into 18 postal zones, first class mail is carried by rail, 15 maritime lines carry international mail, correspondence is classified, mail orders are issued, mail agreements are signed with various countries; General Post Office Direction becomes General Post Office Administration, and in 1902 construction of the Postal Palace begins under the direction of the architect Adamo Boari, and Gonzalo Garita.
In 1926, the third Postal Code is established. In the middle of the century, precisely in 1953, the Postal Guide is published, and clarifies more exactly the activities and attributes conferred upon each office of the General Post Office Direction.
At the end of the last century, changes in postal policies and strategies begin in Mexico: in 1981, the country is divided into sections and each is assigned a Numerical Postal Code. Postal automation is begun in 1984.
By presidential decree and published in the Official Gazette on 20 August 1986, the decentralized organization denominated Servicio Postal Mexicano is created as the answer to the need to modernize both operational and administrative practices in pursuit of greater productivity in the provision of communication services. By this means the organization acquires legal status and property. One of its first acts as an independent entity was to determine its organizational structure appropriate to its new status. To this end, its first action was the substitution of its 9 Regional Postal Managers with 31 State Postal Managers, establishing improved conditions to maximize postal services benefits to its users, passing on jurisdictional decision-making faculties to the 31 State Managers.
In order to improve the organizational structure of the Mexican Postal Service, establishing a balance within its fundamental areas, on 1 February 1989, reorganization was authorized, extending existing functions. For this purpose the Commercial Directory is created; it absorbs the functions of the Directory of Planning and Systems which is abolished, and new departmental-level areas are incorporated to develop basic functions in support of organizational objectives, addressing aspects relative to quality assurance, customer service and works control, among other functions not provided for previously.