No useful threading in Slack, which is still one of its silliest issues. You must be using a paid version of Slack to see messages from a long time ago, as they have a limit on the no-cost version. This probably makes you dependent on your employer. When one switches between channels in Slack, oh boy is that think laggy! Sometimes I can wait for 5s, before the thing has switched, on a fairly modern CPU and up to date browser. In Thunderbird I can switch to saved searches and folders seemingly no matter how many e-mails I have in there in what seems to be perhaps 100 milliseconds. Lets face it: Slack is hopelessly bloated slow and laggy to no end. E-mail does not have these issues, if you use the right tools, as in not using anything like MS Office 265 Outlook to access e-mails, because that is broken in similar ways.