I think it's the only idea ... what other alternative is there ?
Not "encryption" since that's not the problem we are trying to solve - you can do that with gmail right now. I'm talking about the "I woke up this morning and my email was delivered to the local DA and I had no idea and played no part in it" problem ...
Or the, "Chinese hackers dragnetted my account after they found a hole in GMail". Something to be said for being a small fish when the big boys go at it.
Some people are not able to keep up with best current practice to ensure that email from their server is deliverable.
Running your own email server is for many people a sub-optimal solution. Sure, for a small number of people it's a great idea.