Final answer:
European countries commonly use two-letter country codes, based on ISO 3166-1 alpha-2, to designate the destination country on mail, ensuring smooth international mail sorting and delivery.
Step-by-step explanation:
Many European countries use a two-letter country code to indicate the country of designation on mail. These country codes are part of an international standard known as ISO 3166-1 alpha-2, which is used not only in Europe but globally to facilitate the sorting and delivery of mail internationally. For example, France uses 'FR', Germany uses 'DE', and the United Kingdom uses 'GB' for Great Britain. This standard helps to ensure that mail is efficiently routed to the proper destination.