Possible Clues:

• It's a far-reaching message, on paper
• Post needing services of a high-flyer
• Par avion
• Flying post?
• Its first stamps were issued in 1918
• Highly moving letters from survivor he heard
• Communication means since 1911
• No fun in strangely unfamiliar posting abroad
• Chap in Scottish resort’s spoken of postal system
• Postal system first-rate? Complain bitterly about modifications, primarily