I just gave you one example of a use case. It's hardly unique. There are plenty of time-sensitive messages sent in business settings, and plenty of people who don't necessarily want to acknowledge receiving them.

More examples, off the top of my head:

• Manager tells worker they need to cover an emergency on the weekend, worker claims they never received the message.

• Business wants to cancel a work order, contractor shows up and says they weren't properly notified of the cancellation.

• Supervisor sends disciplinary note to employee before dismissal, employee says it was never sent and then claims wrongful termination.

And of course, this has nothing to do with email. So if you set up a "spam filter" that deletes your boss's messages, that's on you. They know they sent you the message, even if you delete it or otherwise pretend they didn't.

This is about an independent audit trail, not "keeping logs". Your personal email server doesn't count, because you can alter the log to show whatever you want. Nobody is going to take your word for it.

Finally, it's pretty clear you have no idea how this system is supposed to work, because you keep claiming that documents are "accessible by any third party". You do understand that not every blockchain system is public, right?