The mailsort reference/number/code located to the right or found under an address on a paper driving licence was devised by the Royal Mail. It is used exclusively for the automated sorting of mail. The first three digits of a mailsort code is the Residue Selection Code. It generally corresponds to one postcode area. The last two digits is the Direction Selection Code, which refers to one or more postal districts.
Mailsort codes often have a letter (A-P) prefix linked to the country’s sixteen regional divisions. It ensures that a sender’s items with the furthest to travel will be processed first by the Royal Mail and ones in the same region as the sender are handled last.
29 million addresses are now affected by the latest Royal Mail delivery scheme. Post is currently being left with neighbours if a recipient is not home. Neighbours and homeowners can refuse to participate by attaching an opt-out sticker next to their letterbox. An electronic opt-out system could be implemented in the future.