Editing Mailsort (section)

==Structure==

The first three digits, the ''Residue Selection Code'', corresponded to an area which can vary in size from one postal district to several [[List of postcode areas in the United Kingdom|postcode area]]s, although most codes correspond exactly to one postcode area. For example:

*406 corresponds to the KA and ML postcode areas; 
*451 and 452 correspond to the LS postcode area;
*491 corresponds to the London SW postal area; and 
*502 corresponds to the BN postcode area

The last two digits, called the ''Direct Selection'' code correspond to one or more [[postal district]]s.

Mailsort codes were sometimes prefixed by a letter (A-P) which corresponded to sixteen regional divisions of the country, although the letter did not form part of the mailsort code. The letter prefix was used by the sender to ensure that when mail was presented to Royal Mail those items with the furthest to travel were given and processed first while those in the same region as the sender were dealt with last. When mail was presented to Royal Mail it was therefore not given in strict mailsort sequence and furthermore the sequence used would differ from one location in the country to another.