It appears to be working from my IP. Per nullindividual's comment do you have a special account setup with them?<p><pre><code> dig @208.67.222.222 +noall +answer -t ns slack.com
slack.com. 1613 IN NS ns-166.awsdns-20.com.
slack.com. 1613 IN NS ns-606.awsdns-11.net.
slack.com. 1613 IN NS ns-1493.awsdns-58.org.
slack.com. 1613 IN NS ns-1901.awsdns-45.co.uk.
dig @208.67.222.222 +noall +answer -t a slack.com
slack.com. 60 IN A 35.82.91.193
slack.com. 60 IN A 44.234.235.93
slack.com. 60 IN A 44.237.180.172
slack.com. 60 IN A 52.89.90.67
slack.com. 60 IN A 54.70.179.16
slack.com. 60 IN A 54.71.95.193
slack.com. 60 IN A 54.188.33.22
slack.com. 60 IN A 54.245.50.245
slack.com. 60 IN A 35.81.85.251
dig @208.67.220.220 +noall +answer -t ns slack.com
slack.com. 288 IN NS ns-166.awsdns-20.com.
slack.com. 288 IN NS ns-606.awsdns-11.net.
slack.com. 288 IN NS ns-1493.awsdns-58.org.
slack.com. 288 IN NS ns-1901.awsdns-45.co.uk.</code></pre>