Thanks for that answer.
Re: the privacy benefits, is it just that Google (or whoever) has no access to your mail, or is there another benefit? I'm not doubting, just trying to understand specifically what you protect against? And how much is the benefit diminished, if at all, if most of your correspondents are on a BigMailServer?
Google not having access to your email is a huge privacy benefit. Even with email becoming less important, most online services still rely on email for sign up and things such as password recovery. You probably also still receive email receipts for flights and online purchases. These are all data points that I would rather Google/Apple/Microsoft not have.
Besides privacy, running your own server means you can create as many mailboxes/aliases as you like. I give each website/company a distinct alias; this allows me to revoke an alias that becomes problematic, e.g. due to spam. There are no storage limits other than those dictated by your hardware, no maximum attachment size, etc. I am immune to "terms and conditions" changing overnight that suddenly shrink my storage or put features such as IMAP access behind a paywall.
Tbh no one really corresponds over email anymore. And most email is sent via Amazon and other email services. So I guess Google can’t read your receipts and bills anymore.
But the main benefit of moving your email off Google is they can’t nuke your email account when the AI decides you are a bot or whatever.