Possible Clues:

• Boatman, say, rejected post
• Nuisance addressed by solicitors
• Unsolicited post, such as advertising etc
• Unsolicited advertising material
• Bodyguard on vessel, the post nobody wants
• Just half spike needed to secure kilometre post to ditch
• Third-class letters often just addressed to 'resident' or 'occupant'
• Many ad circulars
• Reject post offered verbally by man on board in Chinese company?
• Many ad circulars (2 words)