This is for Bobby (not the Forum Dad but De La Rue).

During 1905, mail from India to Singapura were sent by 10 different seamail routes.
1. Kolkata to Singapura via Pinang as part of Kolkata-Hionggong/Hčunggóng Line by
Apcar and Company Opium Steamers
(disgraceful history)
2. Kolkata to Singapura via Yangon and Pinang by
British India Steam Navigation Comapany mail steamers
3. Mumbai to Singapura via Kolamba as part of Marseille-Yokohama Line by
Compagnie des Messageries Maritimes mail steamers
4. Mumbai to Singapura via Kolamba as part of Mumbai-Yokohama Line by
Nippon Yusen Kaisha mail steamers
5. Mumbai to Singapura via Kolamba and Pinang as part of Trieste-Kobe Line by
Österreichischer Lloyd mail steamers
6. Nagappattinam to Singapura via Pinang by
British India Steam Navigation Comapany mail steamers
7. Tuttukkudi to Kolamba by
British India Steam Navigation Company and thence to Singapura via Pinang as part of Napoli-Shanghai Line by
Norddeutscher Lloyd mail steamers
8. Tuttukkudi to Kolamba by
British India Steam Navigation Company and thence to Singapura via Pinang as part of London-Shanghai Line by
Peninsular and Oriental Steam Navigation Company mail steamers
9. Tuttukkudi to Kolamba by
British India Steam Navigation Company and thence to Singapura as part of Marseille-Yokohama Line by
Compagnie des Messageries Maritimes mail steamers
10. Tuttukkudi to Kolamba by
British India Steam Navigation Company and thence to Singapura via Pinang as part of Trieste-Kobe Line by
Österreichischer Lloyd mail steamers
This is a VAST subject and specialized collection can be formed on India to Singapura Maritime Mail Routing.