They don’t just block based on IP, they also do deep packet inspection so if you use say, the OpenVPN protocol without changes, it can be blocked even on a private server.

Outline uses Shadowsocks (socks5 proxy) instead of OpenVPN, which makes it harder to detect.

https://shadowsocks.org/en/index.html

There were several reports that DPI can detect shadowsocks. For example http://ieeexplore.ieee.org/document/8048116/