Control over the domain is 100% my biggest anxiety with mail.
I use Outlook with a family account, and they used to allow custom domain aliases. All of my email is addressed to addresses on my domain. It's actually a pretty good value for 4 people.
If they ever decide suddenly I'm out or they're out, I'll spin up a mail server somewhere else while I figure out my next move
Effective today (November 30), the ability to create new addresses has been disabled.
They’ve been working hard to remove features from that capability. I assume it was either more than they could justify based on adoption rates, a nightmare to maintain, or seeing more abuse than they want to manage.
My anxieties over email match yours. I used to run my own email server but the entire IP range I was in got blacklisted by Proofpoint, and they were thoroughly uninterested in helping unless I owned the entire IP range and could prove it. The ISP didn’t seem to care, and at the very same time Microsoft added the same range to their lists, which meant I wasn’t able to correspond with an attorney. That was in June and by August I’d moved completely to Fastmail. I haven’t looked back, though I do sometimes miss managing my own email server.
A solid intermediate solution is to have your own domain and host your own email server for incoming email. Then google/microsoft/yahoo/et.al. will never be able to lock you out of receiving important email.
You can still use a third party to relay outgoing email if you're worried about deliverability like in your example. But you'll never get locked out of receiving.
I use Outlook with a family account, and they used to allow custom domain aliases. All of my email is addressed to addresses on my domain. It's actually a pretty good value for 4 people.
If they ever decide suddenly I'm out or they're out, I'll spin up a mail server somewhere else while I figure out my next move