Possible Clues:

• As postman, terminally, ill: 'I am unable to deliver it'
• Old-fashioned communication in rhyme
• Modern jargon for letter post, mollusc-slow compared to electronic transport
• Stamped correspondence
• Name penned by royal chap, say, in old-fashioned correspondence?
• Hill's thorn-bound 7am delivery service?
• Conventional (slow) post (informal)
• Householder, a man (say) in traditional post
• Stuff in a box on the street
• Is confused with manilla envelope's content?