I agree. My work has both an unofficial slack and official email. Email is for the serious, no nonsense posts. Slack can have a mix, but with the understanding

I agree. My work has both an unofficial slack and official email. Email is for the serious, no nonsense posts. Slack can have a mix, but with the understanding that it is more informal. We do not pay for slack, so this informality is enforced by the message/content being unavailable as we go on.