Slack appears to be having issues for some people, with reports coming in of users who can’t connect to the service, receive errors when trying to send messages, and can’t even access Slack’s website. The issue doesn’t appear to affect everyone, and Slack hasn’t gone as far as calling it an outage on its status page. The differences in experiences pointed to a possible routing issue or the even more likely culprit, DNS
At 3:50PM ET, Slack says it’s a DNS issue and that your ISP may need to change its settings.
Some of my co-workers have had issues today, while it’s working fine for others (including, unfortunately, me). It’s unclear how widespread the issues are — DownDetector only shows a thousand or so reports.
If you’re still having issues connecting, then either you or your ISP may need to flush your DNS information. One way to get connected if your ISP’s information hasn’t been updated is to use alternate DNS servers, like Google’s ( 126.96.36.199 and 188.8.131.52) or Cloudflare.