Related Clues:

• It's a far-reaching message, on paper
• High-class transport carrying missives primarily?
• Letters dispatched in fliers
• Broadcast produced by man of letters in overseas post
• Postal category
• Stamp on an envelope [and 16-Across flipped]
• Speedy delivery option
• Messages necessarily sent up in this?
• Post up?
• Put on the radio, say, man on the radio offers news from overseas
• Communication from one who should inherit (masculine), so it's said
• Strain with money trouble in post overseas
• Correspondence on the up?
• 'Par avion' letters
• "Par avion" letters