> With IRC, there is no simple, just-works-for-non-techies way to receive messages if you aren't online; running irssi in tmux is not such a solution. No proper history to scroll through to catch up on what's happened on your day off, or search for that analysis summary someone posted back in June.

With the ability to stay online 24/7, why would you go offline? My work machine stays on all the time and I had no problem scrolling back through messages that were sent when I wasn't there. As for the analysis summary example, how easy is it to search for a post that was made half a year ago? Would it be easier to find if that had been sent via email?

> No way to embed images or code snippets in a way that makes them visible without clicking a link or DDC-sending things.

With my current settings using Slack, I have to click on the image link to expand it. Otherwise, I would have a window with multiple animated gifs running in the background to serve as a signficant distraction. Slack also seems to have a low limit on the number of lines you can post in a code snippet. At least a lot lower than what pastebin allows in my experience. And the new WYSIWYG editor made posting them far more annoying than using pastebin and pasting the link.

> No custom emoji

I actually disable rendering them with my current settings in slack. For :), I see :slightly_smiling_face: instead. Animated emojis, like gifs are distracting to me.

> Security and data protection are terrible by default in all ircds I know.

There's nothing that prevents applying company security policies to the servers that are running ircd on site. On the other hand, if Slack suffers a data breach, then what will your company do?

> It's harder to get alerts sent to IRC; everyone and their mother offer Slack integration nowadays, and you can literally curl some text against a webhook if none is offered.

Not everything needs to be sent via a HTTP request. There are plenty of tutorials out there to write a simple IRC bot that can handle the scenario of sending messages to an alert channel. This blog compares the Slack way with setting up an IRC bot: https://drewdevault.com/2018/03/10/How-to-write-an-IRC-bot.h...

> No emoji reactions, e.g. checkmark on someone else's request to say "I did this, everyone else don't bother"

What's wrong with just sending an actual response?

> No treads, like for "I just finished this analysis, this is the summary, details in thread" – extremely useful.

Threads? If I want threads, I would stick to email or usenet. Websites like this one and Reddit largely implemented threads correctly such that they're useful. Websites like Slack and Facebook did not. Having a single level thread under a response with multiple subtopics within that thread makes it much harder to follow what's going on in an otherwise threaded conversation.

> No functioning way to edit or delete messages for everyone after the fact

I've always used the convention of posting a sed style subtitution command right after I realize my error. E.g.,

s/subtitution/substitution/

I think it's easy enough. A different convention is to just post the correct spelling with an asterisks. Every chat client I've seen worked that way without any issues and people understood what the correction was for.

FWIW, I've used IRC, AIM, MSN messenger, and other proprietary messaging clients and platforms and none have been as sluggish and unintuative to use as Slack.