I use my own domains, with registration and dns hosting from a reputable registrar, and paid-for email hosting from a reliable company that offers good support. SPF etc records properly set-up, including on domains that don't accept emails.

For the above: recovery email addresses (different email provider) set-up, 2fa enabled, multiple yubikeys for authentication, with fallback to authenticator codes synced to multiple devices, with fallback to recovery codes stored in multiple locations. Pay yearly for services, renew domains multiple years ahead. Reminders in my calendar to check that renewals have gone through successfully.

Periodically (couples of times a year max) back-up email to local storage using imap.

Some vendors allow fallback / secondary email addresses. There is a process for getting a domain back. I've never been through it but I hear it is painful and not guaranteed.

My process is to pull all emails off the server daily so that if I lose my email account or domain then instead of trying to switch back to my self hosted solution I just get a new domain, a new email provider and update them in each vendor if I still can. In some cases it will require getting on the phone with someone but I do not have much of a digital footprint. I have cut ties with most vendors that are not within a 5 minute drive. The exceptions being the IRS and Amazon, both of which I could live without and I have secondary contact info in the IRS system plus they like money so they will help me.

I self host, and back up emails locally. Done this since 2011, not that difficult (I must donate to Postfix and Dovecot projects!). To fetch emails I use K9 mail on my mobile devices, and thunderbird anywhere else.

I renew my essential domain names in 10‑year increments. As long as I control the domain, I can spin up new mail hosting if any provider boots me. I’d lose the old messages stored on their servers, but the address itself keeps working.

Locally host your own email!

Run your own mail server. Or several of them. No more expensive than running your own website(s).