Measuring QQMail's automated email censorship in China

Desiring to control political ideas shared within its borders, China fosters its own domestic Internet communications platforms where it can better enforce its laws and more tightly control political expression. Access to foreign platforms failing to comply with China's requirements on speech restrictions are often wholesale blocked by the country's national firewall. However, some technologies, such as the Web and email, are too universal to wholesale block and are restricted discriminately. While China's restrictions to Web access have been extensively studied, our work provides a look into email censorship in China.

In this work, we study censorship on Tencent's QQMail, the most popular email platform in China. We introduce a technique to test whether QQMail automatically censors a message, without requiring control of any Internet endpoints in China or any accounts on the QQMail platform, finding 173 combinations of keywords that trigger automated censorship of multiple political topics. We also discover that some censored keyword combinations have extenuating keyword combinations, any of whose presence disables the corresponding censored combination's censorship. Many of these extenuating terms are as politically sensitive as the censored combinations they are extenuating. We find that the motivation behind such extenuating terms is puzzling, defying easy explanation.