Heilbronn (dpa / lsw) – In the internal mail distribution center of a company in Heilbronn, letters with an unknown liquid were discovered on Wednesday afternoon. According to the police, three employees who were in the room complained about respiratory problems and were treated by a doctor. As a precaution, all people present were taken out of the building. However, the fire brigade could not find any dangerous substances. After the distribution point had been ventilated, the employees were able to return to the building. The letters are now being examined by the police. The investigators gave no information on the type of company.