The world’s biggest mail-order shopping company, Otto, said Wednesday it planned to cut as many as 500 of the 3,000 jobs at its corporate headquarters as a result of a weak retail market. The company said it would avoid firing employees and instead rely on attrition to slim down its payroll. Otto officials also said they would seek to cut administrative costs by 25 percent, including major reductions in employee travel expenses. During the past year, the company rang up sales of €19.19 billion, a 0.8 percent decline over the previous year.