Saying that setting up an email server is "simply beyond the scope of nearly everyone" is... Well, it's a bit sad, if you honestly believe that. At the same time, it's also pessimistic and disingenuous. It's disingenuous because you do a thing that some people might incorrectly generalize as, "simply beyond the scope of nearly everyone," even though we all know that there are lots of six year olds are learning Python. Granted, there are likely more six year olds learning Python than people in general learning from scratch to stand up email servers, but we both know that your characterization is quite stretched.

So let me ask you, since your post carries a similar sentiment as many others: Why do you feel that you should express a dismissive opinion about the practice when you've also made it clear you have no inkling to want to do it?

For your information, I set up a how-to to show people how to set up an email server from scratch. No, it's not wildly popular, but several people have used it and have written to thank me, so I don't agree in the least that it is "simply beyond the scope of nearly everyone," and I also have evidence that this is clearly not the case.

To answer your questions, not having my emails crawled is just one benefit, but it's a very important one. Plenty of people say crazy and ignorant things like, "I have nothing to hide," not realizing that it's not about that - not even a tiny bit. If we dismiss the fundamental right to privacy because we have "nothing to hide" right now, we can't later on get privacy back. But, obviously, this isn't a concern of yours, and most people can't consider how the principle applies to historical lessons or how it applies to a possible path to totalitarianism.

So what ARE the benefits? I mentioned that my email servers are deterministic. I can say with precision why a thing happened or didn't happen. Now it may be true that writing Sendmail rules is "simply beyond the scope of nearly everyone," programmers included, but the option is there to decide, again with precision, what I want my servers to accept or reject. I even wrote my own Sendmail rules to refuse email from servers that lie about their HELO / EHLO, or, optionally, only accept from servers where the HELO / EHLO name resolves to the connecting IP. Add procmail to the mix, and now you can have rules than programmers can easily create and change.

Another benefit is precise control of all of my email information. If I delete something, I can be sure it's deleted. It's my information, and I want to control it.

Is my server (well, servers) really more secure than Google's or Microsoft's? Unambiguously yes. Microsoft only ever ends up in a state of relative security after long periods of trial-and-error while non-technical managers come up with design goals which are antithetical to security, bad things happen, then those same non-technical managers demand adding security as an afterthought. Google, I believe (and really, we never can know all that much), genuinely tries to get security right, but how many employees do they have? How many have access to private data?

Take a clean, concise, easy to understand OS, install it on a non-x86, non-IPMI, non-VM computer, install a minimum of things to run only what it's intended to run, do so cleanly without extra cruft or OS specific idiosyncrasies, keep up to date with security vulnerability announcements, and colocate in a trustworthy place, and yes, my servers are definitely more secure than Google's or Microsoft's.