I think business doesn't actually want Email, it wants NNTP. The semantics are different enough that both models have a reason to exist and complement each other:
- With email you write to a specific address. With NNTP you write to a group. In a business you almost always want to target multiple people, because activity is interesting (and relevant) to many people.
- To solve that we have a hack that is mailing lists; they work, but still only allow people to receive content _if they were in the recipient list from the beginning_. With NNTP the actual users are abstracted from the recipient, which allows people to read content in a group _even in the past_, or unsubscribe from a group and not bo bothered by new content
- Because it is ingrained in the protocol, creating/modifying/removing groups is easy to do, contrary to mailing lists. You don't need a special team to do that. Many times there is some content that needs to include multiple lists, but not everyone in those groups is relevant to the discussion... but you still include the different maliing lists because "that's the people who _might_ be interested". No more CC forwarding ad nauseam.
- Side-effect of having well-defined groups: because groups are more fluid they match better to actual people, and so the groups becomes a good denominator of what the "mail" might be about and whether it is important or not (compared to a sender and 189 random recipients)
Just look at the way the latest business IMs like Teams are working. They might not be perfect but they map much more to NNTP semantics, and have become the preferred way to communicate, even in long-ish form, rather than email.
(They do have one big advantage over NNTP though: message editing)
At this point, if a new software is needed anyway, we might as well ditch email and use a better protocol (even if it is not NNTP)