It needs to be said that you can get most of the benefits of your own mail-server and still route outgoing SMTP through a provider like mailroute/sendgrid/mailgun/AWS/even google.

It’s not an all- or nothing question.

Similarly, if you’re worried about the risk of potentially losing incoming email if you have issues, you can keep your existing mail provider choice as fallback in the DNS and fetch+delete mail going there into your primary mailbox every 5 min or so using mbsync.

I have used both pm and migadu with custom domains. Miguda ends being much better on that front feature, pricing, and ease of use wise.

https://www.migadu.com/pricing/

You do lose the layer of encryption protonmail provides. But it is essentially boils down Encryption at Rest and e2e when between two protonmail users. It can be mimicked by pulling down the mail from the servers to your machine and using pgp.