When underpaid mail is detected, Hongkong Post will levy a surcharge on the sender for local mail that bears a sender’s address. For local mail without sender’s address and inward item that bears insufficient postage, the addressee will be required to settle the surcharge payment. Airmail items bearing insufficient postage will be sent by surface route without giving prior notice.
The sender/addressee will receive a notification with an image of the underpaid item enclosed. He/she can settle the surcharge online by credit card or other electronic payment means on the Hongkong Post website according to the instructions stated in the notification, or pay at any post office by presenting the notification. Delivery of the mail will be arranged after the payment is settled.
If the payment is not yet settled within 14 working days, the sender (if given) will be required to collect the mail from the Kowloon Bay Post Office; otherwise, the mail will be disposed of as an undeliverable item, or returned to the postal administration of origin (for inward mail).
For further details about surcharged mail, please click this link.