I've spread my life around several email providers, including myself. I have at least 50 email accounts (inc pre-Microsoft Hotmail).
In the last 10 years, I've lost access to ~5 accounts, usually when the provider axed their free offerings (is fine). In every case, I had warning and time to switch.
If I lose access to one w/o warning, it would be a problem but not catastrophic.
In short: What is the trivial solution to not risking sudden catastrophic loss of email? I don't think there is one. The answers are high-effort, high-maintenance. Technical ability can lessen that some.
note: The reason I don't lean into self-hosted mail harder is spam filtering. I've hosted mail for small biz and have put many, many hours into reducing spam. On top of the usual edge solutions, I write scripts to help mitigate spam and malware campaigns.
But the more visible my domain, the more anti-spam work is required and that state only ever ratchets one way.
In the last 10 years, I've lost access to ~5 accounts, usually when the provider axed their free offerings (is fine). In every case, I had warning and time to switch.
If I lose access to one w/o warning, it would be a problem but not catastrophic.
In short: What is the trivial solution to not risking sudden catastrophic loss of email? I don't think there is one. The answers are high-effort, high-maintenance. Technical ability can lessen that some.