What does Cedex mean on letters?

Ever wondered why some bodies have Cedex as a part of their address?

Courier d’entreprise à distribution exceptionnelle is a service offered by La Poste to businesses and official bodies allowing them to have their post given priority.

The addresses include a special post code (for one very large business or for a group of smaller ones) plus the commune name, then the word Cedex.

A final number (eg. Cedex 2) is used in some cases, notably where there is more than one special Cedex sorting office in the area.