I don't see much benefit from slack over IRC, but definitely over mail. mail threads are horrible, it's impossible to sort incoming by topic, quoting in replie

I don't see much benefit from slack over IRC, but definitely over mail. mail threads are horrible, it's impossible to sort incoming by topic, quoting in replies is quirky, I can't bookmark mails well (at least not when forced to use outlook) and people abuse it as a to-do list making them forget anything that is not a mail... I really like the forced threads in this one other slack competitor though (forgot which), there everything is a thread by default. What I recommend for slack: star all persons and channels that are important, mute any channel with bots, notications only for mentions, occasionally go DND and edjucate people that they can overide it DND with a PM. If you need to have it as a to-do: use the star function on messages.