The Canadian postal code system was introduced by Communications Minister Eric Kierans in February of 1970 although a numbered zone coding system had been in use in some major Canadian cities to varying degrees since 1925. Toronto was the first Canadian city to use a numbered zone and the system spread to other major cities in 1940. The new 6-digit postal code was rolled out over a four year period starting in the test city of Ottawa and the rest of Canada by the end of 1974. The new postal code system allowed Canada Post to speed up and simplify the flow of mail in Canada. The union held a protest of the new postal code system asking for a boycott and ensuring any mail without postal codes received priority treatment. The boycott was called off in February of 1976.
The Canadian postal code system is comprised of 6 digits in two groups of three separated by a space. The format is letter, number, letter space number, letter, number. The letters are capitalized. The first three digits is the Forward Sortation Area (FSA) and the last three digits are the Local Distribution Unit (LDU). Canada is broken into postal code districts which is the first letter of the FSA. The code district begins with A (Newfoundland Labador) and moving westward from the Maritime provinces through the alphabet. So any postal code beginning with P is northern Ontario while R is Manitoba. The LDU represents a range of addresses within that unit for hand delivery. One side of the street may have a different LDU than the other side depending on the location.
Mail not address correctly with the postal code is returned asundeliverable. As a result a large number of letters to Santa were returned. In 1983 the Santa Clause letter response program was initiated with the special postal code H0H 0H0. Canada Post has hard copy and online resources for easily looking up Canadian postal codes.