China Telecom blocking email access?
For months, every time more than a handful of connections were made between my ex-employer's office in Shanghai and their email server in Hong Kong, the latter would become unreachable, not just for email but for web access as well. The strange thing was that access to the rest of the Internet would be untouched.
This prompted me to experiment with ways to circumvent the ISP's port blocking restrictions.
The fight was on!