Postal codes in the Netherlands, known as postcodes, 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 starting 2005. The letter combinations 'SS', 'SD' and 'SA' are not used because of their associations with the Nazi occupation of the Netherlands. Stadsregio AmsterdamPostbus 6261000 AP Amsterdam