Also, when building services that are expected to send HTML email, make sure to generate a plain text version of the content and put it in the appropriate multipart section of the message. Otherwise, people reading in plain text won't see it unless they're willing to jump through hoops to do so (and there's a good chance they'll toss it in the trash instead).
Bonus points if the plain text part is formatted well.
Notice: Use of IMAP and SMTP, open standards for email clients, is not possible with Tuta. This is not acceptable behavior for an email provider and use of Tuta is strongly recommended against for this reason. Tuta's stated reasons for not supporting these protocols are lies and you would be well served by closing your account there.
Well that's a strong opinion. And yes, 100%, IMAP is not a end to end encrypted protocol so how can they offer it when the server can't read the data?
Mail encryption has nothing to do with how the mail is formatted (html vs plain text).
And the client protocol for fetching the mail from the server also has nothing to do with that.
They just need to tunnel the data and let the client decrypt it. Basically what Proton does with their bridge app. And also basically what Tuta's client does.
They will have access to metadata - otherwise they wouldn't be able to work as email service. That's sufficient to implement those protocols.
The client then would have to bring their own crypto, and you'd probably want the SMTP server to reject mails if delivered unencrypted (though their FAQ says you can send unencrypted mails).
The reason they claim they can't is probably trying to keep full control over what users are doing, in which case I agree - fuck them, don't use services like that.
Receiving email, the service provider has full access to the metadata agreed. The main difference between proton and tuta is what data is kept encrypted at rest.
Proton does not encrypt the metadata, from, too, subject
Tuta does encrypt all of that metadata at rest
The clients are open source, you can do anything you want, you just have to implement it. I don't know where the hate is coming from. Tuta is unique being the only email provider that encrypts all the data at rest, and I want to give them a lot of love for that, I don't understand the hate at all