CEDEX means Courrier d'Enterprise a Distribution Exceptional, which breaks down to special business mail in English. CEDEX should always be written in capital letters.
Addresses in France that have CEDEX in them must always have this included. Businesses with this type of address have specific locations for large amounts of mail delivery and mail without CEDEX will not reach its destination. Also, it should not be added to an address that is not a business or does not have a special mail delivery designation. CEDEX is often followed by a number if the company receiving the mail has more than one location for mail delivery. This can occur when various departments of a business have their own specific address and deliver location.