Proton does have open-source bridges/proxies, so they aren’t hiding these details from us

The issue I talked about was not privacy-wise. It just suck to have to use a package that is not in debian repository just to receive commercial emails. Updates are a pain. And it is the kind of software that people should keep up-to-date.

Proton emails are stored in an encrypted form that goes beyond the simple authentication that is part of the POP/IMAP specifications

Ok, let's talk about privacy. Email will never be secure because it was not designed to be and there are too many issues.

The subject line and other metadata are not encrypted. (from protonmail website). Most of the people use email to register to accounts and for commercial communications, where all valuables informations are in the object of the email.

There are more private way to communicate with people (like xmpp or matrix for example)

We kill people based on metadata. Well metadata encryption are pretty important.

So giving up convenience for 0 security sucks.

Perhaps Thunderbird could be enhanced to support the Proton features directly?

It would be great if there were an add-on for it. If someone knows how to develop it, please do it, it would improve UX a lot.

But it does not solve the issue completely. On mobile, the issue is still there (I know they have an app but I would prefer to have all my email at the same place). Also, if I want to use nextcloud mail, you have to developp an addon for nextcloud now.

Edit: changed the link for the alternative piped link suggested.