Just terrible UX in general, and a very bloated & power hungry client. Search is borderline useless, and it's difficult for me to find anything that was talked about a couple weeks ago (meanwhile I can easily grep IRC logs for things that were said years ago). People at work turned off mobile notifications because they sometimes work, but usually not when you want them to work. I wish we'd just switch to IRC.

What protocol does Mattermost use? I was under the impression that it was XMPP, but I can't find anything that says that now that I'm glancing at it. Did they invent their own as well?

Our company still have a lot of guys on irc so a bridge was put in place to mattermost :)