Clarification on Email "end-to-end encryption" to external recipients?

I am picking a new email service provider, and I want to send emails from my new provider to gmail domains - without the contents being collected by Google. I found info on the topic to be quite misleading/confusing.

My impression from privacy guides is that Proton allows this by supporting OpenPGP “allowing for provider-agnostic E2EE emails”, unlike Tutanota which “can only receive encrypted emails from non-Tutanota email accounts when sent via a temporary Tutanota mailbox” (1). Am I correct in saying this means all contents will be encrypted between Proton>Gmail>Proton, Gmail>Proton>Gmail and Tutanota>Gmail>Tutanota, but not Gmail>Tutanota>Gmail?

Then according to Proton (2), Proton is “encryption compatible with other email services”, whereas Tutanota is not - but according to Tutanota (3), both provide “Easy end-to-end encryption to external recipients” but Tutanota even encrypts the subject line, unlike Proton.

Then according to (4), both Proton and Tutanota allow sending encrypted emails to external recipients, but this means the recipient will have to insert a password to open the mail (hence I’d have to send an unencrypted email with the password?). In other words, sending to Gmail is practically the same with both Proton and Tutanota?

Finally, I’d like to know if Proton and Tutanota are the only services which provide this feature? According to Tutanota, Posteo does not (5) - but of course Posteo’s website boasts of how it encrypts emails to Gmail through TLS (6).

To sum up: Can Proton/Tutanota/other send (and recieve) emails to Gmail wwithout the contents being collected by Google. If so, is this only through password protection, which would likely involve an unencrypted email to provide the password? Is there any advantage of Proton over Tutanota in sending to Gmail?

1 Encrypted Private Email Recommendations - Privacy Guides
2 Proton Mail vs Tutanota: Encrypted email comparison | Proton
3 Protonmail vs. Tutanota: Email comparison
5 Posteo and Tutanota: Email comparison
6 Email green, secure, simple and ad-free - - Encryption

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So my understanding is there’s three possibilities:

  1. Emails sent between two parties supporting PGP encryption. These emails will be encrypted and the server can’t read them. Only the sender and recipient can read them by decrypting them in their email client (e.g. Thunderbird, K9 Mail, Mailvelope). Protonmail is based on PGP, so you can have end-to-end encryption between two Protonmail users, or a Protonmail user and someone else who has manually set up PGP (this is possible on every mail provider, inluding GMail, but only a few ones like or make it “easy” or integrate PGP into their webmail).
  2. Emails sent between two parties supporting a proprietary (not PGP) encryption standard (e.g. Tutanota or Skiff). If two people using Tutanota exchange emails, this will be end-to-end encrypted again and the server can’t read the contents. But it’s not compatible with other providers, so in my opinion very pointless.
  3. This leaves most situations where end-to-end encryption is not possible, i.e. when it’s NOT Tutanota ↔ Tutanota, Skiff ↔ Skiff, Protonmail ↔ Protonmail, Protonmail ↔ PGP, or PGP ↔ PGP. Some mail providers like Protonmail or Tutanota now allow you to still send an “encrypted” mail, but this is basically just a link to a webpage (hosted by Proton/Tuta) that’s sent to the recipient and they have to click on the link and enter the password to see the contents of your message. I wouldn’t really call this an encrypted email.

So, because Protonmail supports PGP and Tutanota doesn’t, you could theoretically send a PGP-encrypted mail to a Gmail user, but 99.9% of Gmail users won’t have set up PGP so in practice it’s a bit irrelevant.

The other value add comes from the mail providers like Proton or Tutanota promising to encrypt all the email you receive on with your password. So let’s say you get an unencrypted email from a Gmail user, then Proton will use your PGP key to encrypt the email when it gets received, before it gets saved for good on Proton’s mail server and appears in your inbox. The same happens when you send an unencrypted email, it’s saved encrypted in the “sent” folder and only gets decrypted with your PGP key in the last moment, so that Proton can’t read the content but the Gmail user can read it without setting up PGP.

The problem with this is that you have to trust them to actually encrypt everything. There’s no technological guarantee. Obviously they have access to the unencrypted email if you converse with someone using Gmail. In fact, German law enforcement had a warrant forcing Tutanota to make (secret) copies of the not-yet-encrypted emails a specific user was receiving from non-Tutanota senders.

tl;dr if you use Protonmail your emails will NOT be safe unless your contacts use Proton too or have manually set up a PGP and you know their public key (I think Proton automates this via public key servers); if you use Tutanota your emails will NOT be safe unless your contacts use Tutanota too

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I see, thanks for your input.

Just to confirm, why don’t consider the webpage password encryption offered by tutanota/proton to be an encrypted mail?

This webpage thing is a huge turn-off from using these services. If it is possible to set up PGP within Google, then it seems setting it up on my Gmail is the only way I can get an email to another gmail user without Google reading it, in situations where I am sending an email to a gmail user with no other point of contact (and will easily ignore a stranger asking to open links or do anything else slightly inconvenient).

Wow, so this is how I will end my week of learning about private emails? Settling with gmail since I have nobody to contact who isn’t using gmail, and using private email will do nothing but increase the chances of my mail being marked as spam according to Google.

With Web Key Directory support on the receiver’s end you don’t need to know their public key in advance, this is why we recommend providers which support publishing to WKD over others on our recommendations. If you have Proton Mail, create a new message and enter my email in the To field, for example: email is not hosted on Proton Mail, and the key for my Privacy Guides email is not in my Proton contacts, but Proton Mail can automatically grab my public key from Privacy Guides’s webserver and send the email with end-to-end encryption, because Privacy Guides is configured to support the WKD standard:


Additional reading:

BTW, Proton does not search public key servers, but if you’ve seen Proton automatically fetch a key before, it was almost certainly using WKD. So this method will never work for emailing a user from Proton for example, because doesn’t host a WKD on their end. This is why it’s important to choose a provider that publishes keys on their domain to a WKD from the get-go if you want to receive PGP encrypted emails (or use a custom domain for your email and publish WKD yourself).