I can confirm that's not the case. We have diagnostic and error reporting functionality built-in which is documented here https://docs.mattermost.com/manage/telemetry.html and can be disabled either through the config file before starting the server or in the UI afterwards.
We have quite a few customers deploying Mattermost in air-gapped environments, so even for the enterprise versions we don't require internet connectivity.
There are some things that may not work without any internet connectivity, such as mobile push notifications, since that requires Mattermost Server to connect to our Push Proxy by default. You can host that yourself but will need a custom Apple/Android mobile app then, and the push proxy still needs internet connectivity in the end to reach Apple/Android Push Notification Services. Also our plugin marketplace may not work and you need to download and upload plugins manually.
So overall, some convenience functions may not work, but overall Mattermost can be deployed air-gapped and doesn't have any phone-home aside from optional diagnostics. Let me know if there are any other questions!
(Disclosure: I am working at Mattermost in Security)
even for the enterprise versions we don't require internet connectivity
That's an odd phrasing to me. I would expect the enterprise version to offer more admin features, so of course that version would have the option to disable the Internet requirements. Can you confirm it's the same for all other versions?
As @jasonblais confirmed, it's the same across all versions. I added this specifically since some software requires internet connectivity for license checks and wanted to clarify that this isn't the case with either Mattermost version, open source or enterprise.
We have quite a few customers deploying Mattermost in air-gapped environments, so even for the enterprise versions we don't require internet connectivity.
There are some things that may not work without any internet connectivity, such as mobile push notifications, since that requires Mattermost Server to connect to our Push Proxy by default. You can host that yourself but will need a custom Apple/Android mobile app then, and the push proxy still needs internet connectivity in the end to reach Apple/Android Push Notification Services. Also our plugin marketplace may not work and you need to download and upload plugins manually.
So overall, some convenience functions may not work, but overall Mattermost can be deployed air-gapped and doesn't have any phone-home aside from optional diagnostics. Let me know if there are any other questions!
(Disclosure: I am working at Mattermost in Security)