While ProtonMail’s marketing has always stood out as over the top self-congratulatory, the reaction of people saying “oh no, I need to find an alternative now” represents a fairly naive understanding of the very nature of communication platforms on the internet, especially email.
There is no alternative here. There is no company that will ever solve the problem, within the existing email protocol, where one unencrypted sender (say, marketing emails) can send to a so-called “encrypted receiver” and not have an intermediary able to temporarily read the emails. This is inherent in the design of the system. ProtonMail is not end-to-end encrypted in this case, and no email provider can be on the traditional web.
There are no alternatives. There is no hard, scientific, mathematical solution to this. The best you’ll get is “soft encryption”—the equivalent of encryption where the third party offering the service chooses the encryption key.
Of course there is an alternative, it's called encrypting your E-mail, and has been around for decades (for example in the form of PGP/GnuPG/GPG/whatever).
That said, having observed its history for the last 26 years, I do not think it is an accident that PGP/GnuPG is so difficult to use, poorly developed, generally marginalized, and has not been adopted by any of the big E-mail software authors.
Think of it another way: if Apple decided to really be pro-privacy today and built support for GPG into its Mac and iOS apps, the problem would be largely solved. But for some reason they do not, nor does any other major software maker.
The reason is not 'some reason', as you seem to be somewhat conspiratorially suggesting. The reason is it would not solve the problem of securing email.
Both Thunderbird and Outlook have plugins for PGP and S/MIME. You can use them to read/send mail from Gmail and Yahoo domains as well.
Edit:
If you're using them for an organization that uses Exchange/O365, the admin would need to make sure IMAP/POP protocols are enabled over TLS/STARTTLS, as opposed to using EAS. However, if you're dealing with mail in an organization, you're probably not using your own encryption keys to being with.
What are the marginal benefits (and costs) of running a Helm over ProtonMail service? I can see none.
The justified concerns the security community has with ProtonMail is: Crypto in the browser is bad (mitigable with Qubes), and How do I know PM isn't serving me a backdoored JS.
IIRC, Helm has auto updated binaries so backdoor-free code isn't a delta. The best I can come up with is: server+CPU observation/isolation is stronger on local hardware relative to PM at the cost of network observation. Hypothetical: "Ok a Spectre-style attack is out, spam emails and let's do some timing-correlation traffic analysis"
There is no alternative here. There is no company that will ever solve the problem, within the existing email protocol, where one unencrypted sender (say, marketing emails) can send to a so-called “encrypted receiver” and not have an intermediary able to temporarily read the emails. This is inherent in the design of the system. ProtonMail is not end-to-end encrypted in this case, and no email provider can be on the traditional web.
There are no alternatives. There is no hard, scientific, mathematical solution to this. The best you’ll get is “soft encryption”—the equivalent of encryption where the third party offering the service chooses the encryption key.