Thirty years ago, China sent its first-ever email.

“Across the Great Wall, we can reach every corner of the world,” the Mail Administration of China wrote to researchers at Germany’s University of Karlsruhe at 9:07 p.m. Beijing time on Sept. 14, 1987.

But instead of bridging the wall, China has since built a new one, in cyberspace — the largest system of Internet censorship, control and surveillance in the world, nicknamed the Great Firewall of China.

Thirty years on, it is extending those controls even further.