[piger]

The open-source version also lack any data retention option, meaning that your only option is to let the database grow indefinitely; you can manually delete stuff from the db, but last time I've checked that was not recommended.

Deploying Mattermost is not ideal, as the server requires write access to its JSON configuration file and will overwrite it from time to time, which makes using any configuration manager pointless: after upgrading mattermost you have to fetch the "updated" configuration file from your server and import it back into your configuration manager (and since it's JSON you might get different key sorting and indentation offset).

Despite the above I like Mattermost and I've been regularly using it for more than 1 year, basically for free.

[the_icelander]

In 5.10 Mattermost added the ability to move the configuration to the database, which solves the issue of having a config.json file. This also has the advantage of versioning your configuration in the database which makes rolling back changes very easy.