The current situation is that we have technical solutions for authenticating smtp sending domains. But there will always be someone who flags an email too quickly or just wants to spite you. Or someone that will send spam regardless (or hack an account, etc...). And so we’re back at square one.
This is especially true for situations (like email) that aren't subject to market forces. Because sending email is so cheap, the return rates can be very small to still justify sending spam. There just isn't any market pressure to keep it contained...
One of my clients is a construction firm specializing with churches. It is not infrequent for them to be communicating about a project with a church - often to a role account (e.g. info@church.org), which is step 1 towards being filed as spam - where the role account is shared with a dozen or more people. The building manager will check the email on Mon, Wed and Fri and every other day there will be a number of well-intentioned volunteers at least one of which will click on the spam button dooming my client's email into the abyss. Weeks later we find the church has gone with a different contractor, as they "could never get a response" from my client.
We will go so far as to donate a new IT/Cloud system to the church (small $$ compared with the project) just to ensure reliable communication. But then they think we are just trying to buy them.
Now my client has a blacklisted domain/mail server IP, and bids they send out are rejected as spam by the providers to other churches.
Makes no difference if we are hosting the mail server or if it is a 3rd party mail service. As soon as a customer is sold, we try and move them off email into a web-application framework for ongoing legitimate communication. Again a lot of resistance.
Also I'd expect all the firms competitors to be using Workspace or 365, so if using them gives no apparent protection, presumably they should be suffering from this as well?