Holding messages is a client side task in IRC. Which works because IRC is a protocol, not a product.

But slack actively makes it difficult to get logs out of it. Can't even save your own messages that you sent when you were logged in.

Easy to stay logged into irc, hard to fix slack's logging problem

just use ZNC. why should us pay for something free?

https://wiki.znc.in/ZNC

Indeed, you're still paying for electricity to run a server somewhere of course. ZNC, Quassel, The Lounge, WeeChat if you want to do it yourself. IRCCloud if you want to pay someone to do it for you.

We used bots to do that, but in todays world it's so easy to just stay logged in all the time, just leave a screen or tmux session running as a background process on a server

Would people pay for for a cloud service that bridged some of the gaps between Slack and IRC. Like notifications and offline message retention. Or would you just use Slack in those cases?

How would you do it without using screen, or bots as you say?

I am using Riot messenger. It can sync both Matrix and IRC accounts.

Link - https://about.riot.im/

I personally use an IRC Bouncer. ZNC for instance is a really good one

You can use the log command and then run in on a screen instance.

This may be inconvenient for some people, but for me this is a feature.