India (Yemen) – Aden
Aden is a port city in modern-day Yemen, which was under British administration from 1839-1967. The port of Aden was captured by forces of the East India Company in 1839 and became a dependency, known as the Aden Settlement, of the distant Bombay Presidency (an administrative sub-division of British India). Aden's ancient, natural harbour lies in the crater of a dormant volcano which now forms a peninsula, joined to the mainland by a low isthmus.
The port lies about equidistant from the Suez Canal, Mumbai (Bombay), and Zanzibar, which were all important British possessions. Aden's location made it a useful base for servicemen en route to the east to post letters. In February 1916, Cyril Sladden set sail from Egypt bound for Mesopotamia. The Sladden family had hopes that he would be able to post letters from Aden, but unfortunately he was unable to do so. The following year, however, Wilfred Brown Constable (brother of Mela), was able to post from Aden.
In July 1916, when convalescing in Simla, India, Cyril said he had heard rumours of a direct mail being established from Aden, rather than going via Bombay, but that does not appear to have happened.