Possible Clues:

• Postal delivery, informally
• Nonelectronic correspondence
• *Old-school letters
• One way to pay a bill
• Is confused with manilla envelope's content?
• Conventional (slow) post (informal)
• Hill's thorn-bound 7am delivery service?
• Name penned by royal chap, say, in old-fashioned correspondence?
• Stamped correspondence
• Modern jargon for letter post, mollusc-slow compared to electronic transport