How do you mean locked out? For non-payment or some other issue?

For issues unknown to the user until they are locked out.

There’s probably no provider, paid or otherwise that you can be guaranteed to be safe with because they all rely on automated systems that can make mistakes. I would say you have more chance for active support if you go with a paid service like Proton though.

Apart from that, redundancy makes sense - don’t rely on a single email provider/service but have several independent email identities with your mail synced across them. This goes for associated data too - the worst part of having your account locked is losing access to your cloud-stored contacts, files, etc.

You could try mail.com or gmx.com. Same software on both.

mail.com is a bit heavy with the adware. gmx.com has more free options (like mail forwarding).

Dunno about support. I'm not recommending, just mentioning.

well,you can buy email hosting maybe on porkbun, namecheap or runbox.com

My mail client is Gmail and my mail provider is Fastmail. Fastmail is great, especially if you have many email addresses.

I love Gmail/Cal but don't trust Google's long term offerings. Fastmail means I have my mail in two locations.

After using gmail since their public launch I am very happy with Fastmail now

I would say that there is 3 important points to your question:

1: Use your own domain, this allows you to somewhat easily move providers. 2: Offline backup of your email. Keep a offline backup of you email, it could just be a desktop client checking email. 3: A paid provider with support, so you can get to talk to someone.

I personally think icloud is a option. Fastmail or hey.com could also be.