Got a little something to say here because my startup is all about this. Worked at 2 $100b market cap enterprises and saw a lot of friction specifically in B2B. For internal collaboration Slack/Teams is pretty much consolidated, but for critical B2B interactions everybody falls back to email (and only secondarily to things like LinkedIn DMs or WhatsApp messages). And here's where the problems with email pile up:

No read receipts Need to know exact address to write to Trees/branches problem discussed by others (CCd late in the game? Good luck making sense of things and no chance to grab attachments) Highly vulnerable to phishing and social engineering (anyone can email you) Grab bag: important messages and unimportant newsletters or notifications are all mixed together Emails with precious/sensitive data can be forwarded to anyone (and everyone) in the planet with two clicks

I could continue but you get the picture. As an early Internet user I still have a soft spot for email but specifically for B2B work I think there's a lot of work to be done, similar to what Slack did for internal collab. My startup is genevabm.com for those who are interested, go check us out!