Yahoo stopped its mailbox service in China today as the US tech company readies itself for a final retreat from the world’s second-largest economy. In a letter, Yahoo advised users to change to other mailbox services and download backup contacts and schedules. Last November, the company said in a statement that it was pulling out of China after operating in the country for more than two decades, citing an “increasingly challenging environment” as the reason for the move. Yahoo, which entered China in 1998, is the latest in a slew of western tech giants, including Google and LinkedIn, that have withdrawn from the country. [GizChina]