They do seem to document what they send: https://docs.mattermost.com/administration/telemetry.html https://docs.mattermost.com/administration/telemetry.html I

They do seem to document what they send: https://docs.mattermost.com/administration/telemetry.html https://docs.mattermost.com/administration/telemetry.html I think this telemetry should be opt-in for self-hosted, but the data they send doesn't seem to push it to the level of spyware (i.e., no message contents or PII as far as I can tell). It's still much more private than Slack.