First time hearing about Mattermost. Good thing I found this article
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Their "threads" feature was also great: it was just like replies in Discord (all go into the channel) but you could open up the thread to get it isolated. Worked way better than slack replies which just devolve instantly into you losing all track and messages can't be found again.
I desperately wish Discord worked like this. As you say, current threads just shove away conversation and it's quickly lost.
My question (and pcthrowaway's) response is about what happens when you send a message inside a thread without replying to a message. I was wondering if it would be sent into the main channel, with no context, which would be confusing.