From:
John Leach's Encyclopedia of Postal Authorities :

D

Dahomey - Duttia

Dahomey - Duttia

Dahomey
Dai Nippon
Dairen
Dakar-Abidjan
Dalmatia (German Occupation)
Dalmatia (Italian Occupation)
Damao
Danish West Indies
Danubian Principalities
Danzig
Danzig (Polish Post Office)
Dardanelles (Russian Post Office)
Das Island
Datia
DDR
Debrecen (Rumanian Occupation)
Deccan
Dedeagh
Dedeagatz (French Post Office)
Dedeagatz (Greek Occupation)
Democratic Federation of Yugoslavia
Denikin Government
Denmark
Deutsche Besetzung Zara
Deutsche Demokratische Republik (DDR)
Deutsche Militarverwaltung Kotor
Deutsche Post
Dhar
Diego-Suarez
Diu
Djibouti
Djibouti (French Colony)
Dobruja (Bulgarian Occupation)
Dodecanese Islands (British Occupation)
Dodecanese Islands (Greek Occupation)
Dominica
Dominican Republic
Don Territory
Dorpat (German Occupation)
Dresden
Dronning Maud Land
Dubai
Duitsch Oost Afrika Belgische Bezetting
Dungarpur
Durazzo (Italian Post Office)
Duttia