Implemented and open-source from Tutanota since 2017.
https://tutanota.com/blog/posts/first-search-encrypted-data

FYI (received from PM today when this was reported as a problem):

"As you have noticed, within ProtonMail, you can only search by subject lines, sender, recipient, and the time of messages. Because ProtonMail uses end-to-end encryption, we cannot read any of your messages or attachments, and therefore we currently cannot search through the message body.

Our developers are currently working on integrating an encrypted body search feature which will maintain the current level of privacy and protection that ProtonMail offers. However, due to the complexity of this feature, at this time, we cannot know for sure when it is going to be implemented.

You have noted, however, that you wish to search for specific To/From addresses. Please note that you can do this through the Advanced Search option which you can access by clicking on the downward-facing arrow next to the address input box."

FYI (received from PM today when this was reported as a problem):

"As you have noticed, within ProtonMail, you can only search by subject lines, sender, recipient, and the time of messages. Because ProtonMail uses end-to-end encryption, we cannot read any of your messages or attachments, and therefore we currently cannot search through the message body.

Our developers are currently working on integrating an encrypted body search feature which will maintain the current level of privacy and protection that ProtonMail offers. However, due to the complexity of this feature, at this time, we cannot know for sure when it is going to be implemented.

You have noted, however, that you wish to search for specific To/From addresses. Please note that you can do this through the Advanced Search option which you can access by clicking on the downward-facing arrow next to the address input box."

Great question. ProtonMail staff: please, this basic function would be swell. Thank you

Word. ProtonMail staff: please, this basic function would be swell. Thank you

How'd that work out for you? ProtonMail staff: please, this basic function would be swell. Thank you

There are a dozen of these requests. Not enough votes in the world to get this feature implemented, evidently. ProtonMail staff: please, this basic function would be swell. Thank you

What Mat said. This is crazy. Seriously--is this some kind of joke that the employees are sitting back and laughing about ("what if we didn't implement the most basic/easy feature and then just watch everyone go berserk?"). Please, why are you making use choose between privacy and basic functionality?

Adding to this that I do NOT want to see results from the trash in my search. I trashed it because I don't want it! It makes more sense for the default to be the folder that I'm in and then the advanced options can add more folders if I choose rather than the reverse.

Hello, this search feature not functioning is really a major problem now, i have to wade through 50 or more mails that have all been merged into the same history. ¨Finding the right email is like looking for a needle in a hay stack.
I really dont have time for this, and disapointed that such a basic feature doesnt work: using names and words which i know appear in the email i need to identify repeatedly comes up with 0 results.
Please HELP ! Thanks

The search is really bad, it even misses e-mails when there's no typos. :/ Hopefully they'll improve it and yes, add support to search the e-mail itself.

This is actually really important and is regularly a frustration for me. :O

It appears the search only looks at the subject line. It would be nice to be able to search inside the contents also.

I'm blown away this isn't a basic feature.

125 votes here: https://protonmail.uservoice.com/forums/284483-protonmail/suggestions/12371181-search-message-body
24 votes: https://protonmail.uservoice.com/forums/284483-protonmail/suggestions/13027677-search-for-keywords-and-phrases-in-the-body-of-e-m
2380 old votes for pretty much same request: https://protonmail.uservoice.com/forums/284483-protonmail/suggestions/15220806-the-ability-to-search-the-contents-of-emails-not

You made this idea PLANNED 6 years ago? How can you deny your users such basic absolute necessity? I wasted hours already finding emails that would take seconds to find if in-body search was a thing for your web app. Every time a new bill comes, I ask myself, why am I even supporting a company that refuses to implement an essential feature that is not even hard to implement. You just wasted resources and time on a new UI but couldn’t be bothered to throw in a quality SOLR based search? Disgraceful.

I can't believe this feature only has 24 votes. It is unacceptable that this is not implemented by default and will be the main reason for moving to a different provider because there is no way to quickly find old emails!

I find Protonmail to have the worst search functionality of any other email client on the market. It consistently refuses to return search results when I know the messages are there. It is the most frustrating part of using Protonmail. For instance, searching for "music" and "notes" - (space inbetween) - nothing is returned. But if I enter "musicnotes" - no space - results are returned. If you don't remember EXACTLY the domain, the subject title, etc. you are out of luck. Search is an old Internet functionality at this point. I would like to think that Protonmail could do better. BTW, turning on "fuzzy" search does ABSOLUTELY NOTHING to return better (or even any) results.

Search email has never worked. Therefore I am eligible for a refund because I paid for something which was not delivered.

there are ~125 votes for an item called "Search Email Body", the same idea, slightly different name.
This is an essential feature!

there are 525 votes for "Search Email Text" and it is indicated as a planned feature. These two are the same idea with a slightly different name. Search for "search " in the search box --->

fully agree! this should be an emergency for the pm team!!!!!!! it's been five years!!!!!!!!!!!! I clearly can't go into a paid subscription until this is available... (which means I'm probably gonna give up on pm very soon since my testing phase has proven that it's not viable for me at the moment without this feature...)