| 28 October 1916 |
|
Accession of States of Johore, Kedah, Perlis, Kelantan and Trengganu to Extradition Treaty between the United Kingdom and Siam of March 4, 1911 |
| 30 November 1920 |
|
Universal Postal Convention (Revision of Convention of May 26, 1906) |
| 30 May 1924 |
23 May 1925 |
Treaty between the United Kingdom and Finland for the Extradition of Criminals |
| 28 August 1924 |
1 October 1925 |
Convention and Protocol revising Universal Postal Convention of November 30, 1920 |
| 28 June 1929 |
|
Postal Union Agreement regarding Insured Letters and Boxes |