Postal codes in the Netherlands
Postal codes in the Netherlands, known in Dutch as postcodes, were introduced in 1977 by the then PTT, now PostNL. They are alphanumeric, consisting of four digits followed by two uppercase letters. The letters 'F', 'I', 'O', 'Q', 'U' and 'Y' were originally not used for technical reasons, but almost all existing combinations are now used as these letters were allowed for new locations from 2005 on.
Source: Wikipedia — Postal codes in the Netherlands (CC BY-SA 4.0)