each FSA in those cities. For cities with a large number of FSAs, applicable neighbourhoods and boroughs are specified. Table of all postal codes All Canadian postal codes are listed in the following links, organized by first letter. Local delivery units The last three characters denote a local delivery unit (LDU). An LDU denotes a specific single address or range of addresses, which can correspond to an entire small town, a significant part of a medium-sized town, a single side of a city block in larger cities, a single large building or a portion of a very large one, a single (large) institution such as a university or a hospital, or a business that receives large volumes of mail on a regular basis. LDUs ending in zero correspond to postal facilities, from post offices and small franchised retail postal outlets all the way up to sortation plants. In urban areas, LDUs may be specific postal carriers' routes. In rural areas where direct door-to-door delivery is not available, an LDU can describe a set of post office boxes or a rural route. LDU 9Z9 is used exclusively for Business Reply Mail. In rural FSAs, the first two characters are usually assigned in alphanumerical order by the name of each community. LDU 9Z0 refers to large regional distribution centre facilities, and is also used as a placeholder, appearing in some regional postmarks such as the "K0H 9Z0" which formerly appeared on purely local mail within the Kingston, Ontario, area. Number of possible postal codes Postal codes use 20 uppercase letters of the English alphabet; they do not include the letters D, F, I, O, Q or U. The first position also does not make use of the letters W or Z. This means the maximum number of FSAs available is 18×10×20 = 3,600. With 10×20×10 = 2,000 possible LDUs in each FSA, there is a theoretical limit of 7.2 million postal codes. The practical limit is a bit lower, as Canada Post reserves some FSAs for special functions, such as for test or promotional purposes, (e.g. the H0H 0H0 for Santa Claus, see below) as well as for sorting mail bound for destinations outside Canada. The current Statistics Canada estimate of over 830,000 active postal codes represents about 12% of the entire postal code "space", leaving ample room for expansion. There is less room with regard to FSAs, however. In particular as