Possible Clues:

• Type of postal service
• Cool guy's oral communication
• Sounds as if, being a man, one inherits the post
• Post in which a musical bloke may be heard?
• Quick way to deliver boy who will succeed, we hear?
• Way of communicating getting musical heroine into trouble
• Top-flight post gives top-rate marines trouble
• Packet on packet? Not if it's this
• Girl's in trouble for high-flown writing
• Fast delivery option