sentences:  Air mail was introduced on 1 April 1928, and the 6d stamp was issued overprinted "AIR MAIL" as Malta's first airmail stamp.In 1928, it was decided that dual-purpose postage and revenue stamps would be issued once again instead of having separate issues.The 1926–1927 stamps were issued with "POSTAGE AND REVENUE" overprints in 1928, and a series of stamps with amended inscriptions was issued in 1930.