Business emails addressed at appointed recipients need to comprise the following information: company name, legal form of the company, commercial settlement, registration court and number of registration within the commercial register. Incorporate enterprises, like limited liability companies or public limited companies, additionally need to add  the managing directors and where required the chairmen of the supervisory board. Failure to comply with these rules can be followed by a penalty payment or an official reprimand with costs.

For information (in german): http://www.heise.de/resale/artikel/84557