Possible Clues:

• Mail order?
• Warning on an envelope
• Mail instruction sometimes ignored, as suggested by the words in this puzzle's circles
• Stamp on a large envelope
• Advice to man of letters, mafia leader, half of Wellington and one of The Kinks
• Bob retires with good books to bed around start of the night - it's advice you'd give to a man of letters
• Sounds like something the spinal surgeon might say in advice for postman?
• Words on a photo mailer
• Envelope direction