Related Clues:

• Post-office stamp
• Messages from on high?
• A sweet French girl I left, being sent overseas
• Top familiar arrangement of surface letters? No!
• Post going by plane
• It's marked 'par avion'
• I'm a liar (anag)
• Letters carried by plane
• Letters that are flown in
• Par avion
• Familiar ground following cut in postal service
• Letters taken by plane
• Two things Charles is but Camilla isn't, in speech to deliver abroad?
• Fast delivery
• To be sick confines girl to such correspondence