Hey there,
I’m on the search for an alternative to Mattermost for a small institution I’m working with. Mattermost was the strongest contender for our needs, yet they changed their policy regarding self-hosted instances. The factor that killed it for us, is the hard cap on 250 registered users, as we potentially might need to commodate more than that.
Rocket.Chat has similar caps.
We found Zulip, and it seems as it might be what we are looking for, but we haven’t tested yet. Nonetheless, I wanted to address this community, as you may have another good idea?
On Matrix, as long as you have your username and password, it’s not possible to get “locked out” due to not having your keys. In fact, your keys are only necessary if you plan to participate in encrypted chats, in which case it’s obvious that losing your key will mean losing access to old messages. However, you will still be able to receive new messages by generating a new key.