I am slowly migrating everything away from my paid ProtonMail account, and I intend to just go back to using a megacorp email... despite absolutely loathing and detesting megacorps. At this point in life, email is simply too important. Notices from government agencies, my accountant, my lawyers, my various banks... I quit self hosting for these reasons (no matter how good I am, I am not full time keeping my self-hosting pristine), and now I apparently cannot fully trust Proton.
The only durable solution for email is:
1. Have your own domain 2. Have a copy of all your mailboxes locally (easily done with IMAP).
With that setup, migrating email is only a matter of opening a new account and changing the DNS record.
Alternatively, another person in the comments here mentioned mailbox.org and I am thinking about that.
I just know I need email I can rely on a little bit more.
But very opinionated and no IMAP.