While we do not block Slack in China from our end, we do know that our content delivery network is very often blocked in China, and so accessing Slack there is somewhat inconsistent.
We are looking into how we can improve the service for our users in China. 
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Any updates on this? My company is rolling out Slack Enterprise and it's be nice to be able to use it at my location on the mainland.
The situation hasn't changed, but depending on your network setup, you may still be able to connect to us from your other location. Sorry we don't have a more specific update for you!