Please look at indexedDB - this is now a mature web tech available in any browser. This makes it completely viable to have a locally decrypted in-browser cache that makes search easy to implement.

Yeah it should be toggle-able for Robert and many others, not everyone wants to cripple their search ability more than it already is.

For me, I don’t mind not having a functioning search if metadata was encrypted.

btw, subject is not needed to deliver the email, at least start by encrypting that Proton! Years of ignoring this won’t help.

Can it be a toggleable option? Also, I would rather have a functioning search than encrypted subject/meta data. If I were willing to sacrifice such a basic functionality as search, I should just use Signal chat instead of email.

What is the use to have users pay for encrypted email if the metadata remain unencrypted and anyone interested can access and follow them to the original sender.

Let's not fool ourselves; Proton mail is neither safe nor private while metadata remain unencrypted!!

Note that almost all ideas from the response from 8 years ago are either debunked or no longer true.

0. The metadata you need to deliver the message is different from the metadata you need to serve the message after it is delivered. Once delivered, all you need is a UUID to identify it, and the entire RFC2822 contents can happily live in an encrypted blob. The difference is whether an adversary sees plaintext headers while the message is in transit, versus plaintext headers for all your historical messages.

1. Subjects are not part of the envelope. Even if it is not a published standard, There are widely-adopted protocols to encrypt subjects. You can encrypt the subject of all outgoing messages, and encrypt the subject of an unencrypted incoming message while still being compatible to most of the world.

2. RFC8551 is already a "proposed standard". You cannot just say the technology to encrypt all headers does not exist. You can encrypt the entire message once it has been delivered to your mailbox, while still being compatible to a proposed standard.

3. One should face the consequence if they opt in to encrypting (just the subject or) all metadata. Yes, it means web-based search becomes useless if headers like "From", "To" and "Subject" are all inaccessible, but you should give us this option if this is a genuine demand from us. There are still legitimate uses of ProtonMail, e.g. a unsearchable web + a local IMAP mirror, in the encrypt-everything configuration. Or you can support limited searching of locally cached messages like what Tuta does.

4. The threat from metadata exposure is real. Subjects of all emails you ever sent & received can reveal a lot about you, even before the age of AI. Even the organizations and people you associate with allows a non-trivial profile of you being built.

5. Homomorphic encryption is indeed "an area of continued research" but please do not allow that distract us from what we can already achieve today.

Very disappointed that in 2025 Proton is STILL not encrypting metadata/subject line... As someone else here has written, of the THOUSANDS of emails I get among all my email services, I NEVER remember a subject line for a search. And even if I did, PRIVACY is far more important to me than search convenience. It discloses far too much info that subject/sender are visible to anyone (or any authority) that gains access to Proton's servers. This is a major issue for me and prevents me from making Proton my main email service provider.

Searches cannot be done by content I guess, because it is encrypted so, what is the point to not encrypt the Subject? I will never understand this.

Searches should ONLY be done by receiver, sender and date. I have multiple personal email accounts (Proton, Tuta, etc) and business email (Microsoft/Outlook). On all my inboxes I had never to search by Subject. When I need to search and email is mostly by "sender" or "date", usually a person does not remember the proper "Subject", is not easy when you got tons of emails per day calling your inbox door.

So please Proton, give it a new review and encrypt the Subject, otherwise subjects like "Mortgage Cancelled" (as example) are heavily leaking privacy!

Tutanota has this aswell, if it still causes issue with the search, it would be nice if you give us the choice to encrypt meta data. Especially the email subject & attachement names.

Metadata encryption makes it safer to store mail and contacts on Proton servers, as all of the stored data would be protected if the account were the target of a search warrant. The competing service Tuta is able to encrypt all metadata for its mail and contacts while offering encrypted search in the browser, and I see no reason why Proton Mail can't do the same.

Mail is inherently unsecure, mainly due to the ecosystem. As answered by Proton, I'm not sure adding extra lyers will help that much, because of the disadvantages (compatibility with the ecosystem, security of the recipient address, ...)

If you need a true secure mail, write only to other Proton users (isolate the ecosystem), it fixes most of your concerns.

But for true secure communications, other more recent protocols exist (Signal, etc...).

I though I've read somewhere that you couldn't do the "automatic forward email" because you couldn't see any informations about the emails ?!

And here it looks like you need this for search ? Am I missing something here ?

This should be moved under ProtonMail Feedback

6 years and counting. Tutanota already has this, and their search is working and their web client is faster than PM's. Not as nice looking though.

E-mails could be indexed locally and search limited to local search. That's the way Tutanota does it.

In fact, Tutanota encrypts all metadata except email addresses and timestamps. From their blog (https://tutanota.com/blog/posts/differences-email-encryption/):
"Tutanota does not rely on PGP to ensure that your data is kept secure. This way Tutanota can also encrypt much more data: body, attachments, subject lines, and sender names. The only remaining data in Tutanota that is not yet encrypted are email addresses and times of emails."

Most importantly, Tutanota also encrypts a user's whole address book, including e-mail addresses and names — the most important info in a contact list. In comparison, Protonmail's contact encryption is rather feeble, given that it doesn't encrypt these two key components.

Meanwhile, a "notice" underlining that the subject field is unencrypted might help the less savvy user.

Please make the subject line encrypted for all PGP emails and for the Non-Protonmail users encrypted emails.

people will forget and therefore the subject which can give away lots of the email details will be send in a insecure way. This will fix this.

would like the subject to be encrypted also

Please use a generic subject name such as "Encrypted email from ProtonMail". Right now encrypted emails will leak the subject which is considered metadata.

As far back as 2018, Enigmail/Kleopatra/Thunderbird/GnuPG has been using the Memory Hole standard to include the subject line in the encrypted portion of the PGP message. ProtonMail has maintained that the use of PGP is what holds them back from encrypting the subject line, but that's not true. Enigmail puts a fake, filler subject line in the header and puts the real subject line text encrypted within the body. What's worse is ProtonMail arbitrarily blocks using Enigmail to encrypt an email with a different PGP key underneath the "normal" ProtonMail key. So not only does Proton not include this subject line feature, they go out of their way to prevent you from using it. I can literally encrypt more in Thunderbird with my Gmail account than I can with ProtonMail's Bridge. That's ridiculous. There is no reason for ProtonMail to dictate to me what I put in my emails. If I want to send a PGP-encrypted email to someone outside of ProtonMail using Thunderbird, that should be allowed. I thought the whole reason Proton gave for using PGP instead of something like Tutanota was to be more compatible with others' PGP encryption. Now they're really doing the exact opposite - worst of all worlds.

When will ProtonMail allow PGP/MIME encryption of the subject line in the same way as Enigmail? It's a huge difference between Proton and and competitors. Proton can do what Tutanota does without leaving PGP. Will ProtonMail at LEAST allow using Enigmail PGP encryption and then add Proton's encryption on top of it, if necessary, so that I can encrypt my subject line if I want? I want to stay with ProtonMail, but being four years behind on this and other things, like full encrypted search, calendar, fully encrypted contacts, etc. that Tutanota offers for a lower price makes it hard to justify. Can we at least get this part fixed? I know calendar is coming, even if the other things aren't.

Thanks for all you have done. I hope to see Proton continuing to grow - happy to be a paid supporter.