I
- Iceland (1873–)
- Ifni (1941–1968)
- India (1854–)
- Barwani (1921–1938)
- Bhor (1879–1901)
- Bijawar (1935–1937)
- Bundi (1894–1941)
- Chamba (1886–1948)
- Cochin (1892–1933)
- Dungarpur (1893–1916)
- Faridkot (1879–1900)
- Gwalior (1885–1949)
- Idar (1939–1944)
- Indore (1886–1941)
- Jaipur (1900–1947)
- Jind (1874–1943)
- Kishangarh (1899–1928)
- Morvi (1931–1935)
- Nabha (1885–1942)
- Orchha (1913–1939)
- Patiala (1884–1947)
- Sirmoor (1879–1899)
- Soruth (1864–1937)
- Travancore (1888–1946)
- Travancore-Cochin (1949–1950)
- Indo-China (1889–1946)
- Indonesia (1950–)
- Indonesia Riau (1954–1964)
- Inhambane (1895–1917)
- Inini (1932–1944)
- Ionian Islands (1859)
- Iran (1870–)
- Iraq (1923–)
- Ireland (1922–)
- Israel (1948–)
- Italian Colonies (1932–1934)
- Italian East Africa (1938–1941)
- Italy (1862–)
- Modena (1852–1859)
- Parma (1852–1859)
- Romagna (1859)
- Roman states (1852–1868)
- Sardinia (1851–1863)
- Tuscany (1851–1860)
- Two Sicilies (1858–1861)
- Campione (1944)
- Italian Social Republic (1943–1944)
- Italian post offices in Africa (1901–1915)
- Italian post offices in China (1917–1918)
- Italian post offices in Crete (1900–1912)
- Italian post offices in Tientsin (1917–1921)
- Italian post offices in the Turkish Empire (1908–1922)
- Trieste Italy (1947–1953)
- Venezia Giulia (1945-1945)
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