What is a certificate of posting? - Royal Mail
A Certificate of Posting is your proof that you have posted the item declared on the certificate into the Royal Mail network. The Certificate of Posting needs to be date stamped and signed at a Post Office® window as having been accepted into the network.
Track & trace | Letters and Parcels | Post Office®
www.postoffice.co.uk › track-traceYour tracking reference number. check icon. To track your item, you will need the reference number found on your Post Office receipt. This may be called a barcode or a reference. check icon. The reference number is between 9 and 27 characters long . check icon. If you have sent your item at a Post Office and you have lost your receipt or tear ...