If you're really concerned about someone stealing your e-mail don't store it on a server! I download all my e-mails to my laptop using Thunderbird, where I store them in an encrypted filesystem. I make daily encrypted backups of the e-mails which I store in the cloud, the encryption key never leaves my device. I keep 3 months of e-mails available online so I can search through them on my phone (which is an acceptable risk for me). IMHO services like Protonmail offer very little additional protection over that.
Few people remember this today but downloading e-mails was the norm in the early 2000s and before. You would only keep a few weeks or months of e-mails on the server and then either delete or download them, as providers didn't offer very generous storage quotas. It was only with the introduction of GMail that this changed because Google offered "unlimited" storage (since they wanted people to store all their e-mails online so they could mine them).
BTW Protonmail doesn't need to inject extra JS into your client and wait for you to login in to decrypt your e-mails, they receive them all in cleartext and they send out e-mails for you in cleartext so they can simply log them without any modifications to the client code.
You can have encrypted offsite backups for cheap a la backblaze (and slightly more expensive with other providers if you have principled objections to backblaze).
Depending on your POV it is either a mild story or a non-story. It certainly doesn't meet my threshold for avoiding a service, but some people are more sensitive.
I'm not trying to protect against state-level surveillance, that would be hopeless IMHO. I'm protecting against a hacker stealing my entire e-mail history from the last 5-10 years.
Few people remember this today but downloading e-mails was the norm in the early 2000s and before. You would only keep a few weeks or months of e-mails on the server and then either delete or download them, as providers didn't offer very generous storage quotas. It was only with the introduction of GMail that this changed because Google offered "unlimited" storage (since they wanted people to store all their e-mails online so they could mine them).
BTW Protonmail doesn't need to inject extra JS into your client and wait for you to login in to decrypt your e-mails, they receive them all in cleartext and they send out e-mails for you in cleartext so they can simply log them without any modifications to the client code.