A basic validation of address data is performed by the .lu registry. The post code must be between two and 16 characters (a-Z, 0-9, space or ASCII dash) depending on the country of the address.

Country Prefixe (optionnal) Number of characters
Austria A- 4 digits
Belgium B- 4 digits
Switzerland CH- 4 digits
Germany D- 5 digits
Denmark DK- 4 digits
Spain E- 5 digits
France F- 5 digits
united Kingdom   Two blocs of letters and digist separated by a space or dash
Ireland   According to the EIRCODE code (Additionnal information on eircode.ie)
Italy I- 5 digits
Luxembourg L- 4 digits
The Netherlands NL- 4 digits, a space, two letters
Sweden   3 digits, a space, 2 digits
United States of America   Two letters (state) followed by a space or dash (all of this optional), then 5 digits, optionally followed by a dash and 4 digits
Bermuda   Two letters, a space and two digits (Additionnal information on bermudayp.com)

For explanations on post codes formats, please refer to 'List of postal codes' WikiPedia webpage.