Slack the company does use Slack the product for inter-company communication. However, their Slack-inside-Slack is a relatively isolated "instance" of Slack on

Slack the company does use Slack the product for inter-company communication. However, their Slack-inside-Slack is a relatively isolated "instance" of Slack on separate infrastructure for exactly that reason. The exact level of isolation/redundancy is not clear to me though. Source: I asked a Slack engineer about this in-person. Maybe a real Slack employee can chime in with more info.