From:
John Leach's Encyclopedia of Postal Authorities :

T

Tadzikistan - Togo
Tokelau - Tuvalu

Tadzikistan - Togo

Tadzikistan
Tahiti
Taiwan
Tajikistan
Tanganyika
Tangier
Tangier (British Post Office)
Tangier (French Post Office)
Tangier (Spanish Post Office)
Tannu Tuva
Tanzania
Tasmania
Tchad
Tchongking (Indo-Chinese Post Office)
Telos
Temesvar (Rumanian Occupation)
Temesvar (Serbian Occupation)
TEO
Terre Adelie
Tete
Tetuan (Spanish Post Office)
Thai Occupation of Malaya
Thailand
Thailand (British Post Offices)
Thessaly (Turkish Occupation)
Thrace
Thrace (Allied Occupation)
Thuringia (Russian Zone)
Thurn & Taxis
Tibet
Tibet (Chinese Post Offices)
Tientsin (French Post Office)
Tientsin (Italian Post Office)
Tierra del Fuego
Timisoara
Timor
Tobago
Togo
Togo (Anglo-French Occupation)
Togo (British Occupation)
Togo (French Colony)

Tokelau - Tuvalu

Tokelau
Tolima
Tonga
Tongking
Toypkia
Transbaikal Province
Transcaucasian Federation
Transjordan
Transkei
Transvaal
Transylvania (Rumanian Occupation)
Travancore
Travancore-Cochin
Trebizonde (Russian Post Office)
Trengganu
Trentino (Italian Occupation)
Trieste
Trieste (Allied Military Government)
Trieste (Yugoslav Military Government)
Trinidad
Trinidad & Tobago
Tripoli (Italian Post Office)
Tripolitania
Tripolitania (British Administration)
Tripolitania (British Military Administration)
Tripolitania (British Occupation)
Tristan da Cunha
Trucial States
Tsingtao
Tunisia
Turkey
Turkish Cypriot Posts
Turkish Empire (Foreign Post Offices)
Turkmenistan
Turks Islands
Turks & Caicos Islands
Tuscany
Tuva
Tuvalu