For intra-corporate mail, email works just great, because the identity problem is solved. Trusted communications between 3rd parties just isn't a natural mail use case.
Not really. Hence the rise of intra-corporate chat software.
People instead prefer to join focused, well defined groups to send and receive intra-corporate communication.
Not bee CC'ed spammed all to h*ll about every little office detail that has zero impact on you and your job.
Spam, in the I'm getting random Viagra emails sense, is being handle very well lately.
That said... We have a very large industry that easily helps you get your "ham" (the mail in-between Spam and mail you really want to receive) inboxed.
This is email from legit companies. Maybe you signed up to a newsletter, maybe you didn't. Maybe you're just getting a cold email. But those emails are inboxed.
People are still complaining about being overwhelmed by their email, even though our Spam filters have improved greatly.
You need to consider what is more valuable, the ability to universally send arbitrary content to arbitrary end points without intermediaries .... Or no spam, and perfect security.
As I said, it's all about identity.