Proton Mail uses zero-access encryption(new window) to store all emails at rest, and emails sent between Proton Mail users are fully end-to-end encrypted. This is good for privacy because it means we cannot read the content of your emails.
You can search the content of your encrypted emails without giving Proton Mail access to those messages. We achieve this by creating a local index of your emails and storing it using your browser’s web storage(new window).
When you perform a search, the app goes through the index of your downloaded emails and highlights all matches.
Everyone who subscribes to a paid Proton Mail plan can use content search.
The index is created in your browser and never leaves it, so no one else, including Proton Mail, can access it without physical access to the device your browser is installed on. Each message inside the index is encrypted and can be decrypted only when you are logged in on the device hosting the index.
This means that when you have search message content enabled, but your web browser is closed, an attacker with physical access to your device cannot read the contents of the index file. If you are logged in with your Proton Mail tab open, a decrypted version is stored in memory, but at this point, they would have direct access to your emails, anyway.
The index of your emails
To search your messages’ contents while keeping them private, Proton Mail creates an index of your emails in your browser’s web storage. However, this means that:
- You must create an index of your messages for each browser on each device that you access Proton Mail with.
- You may not be able to search your messages’ contents if you use your browser in Private (Incognito) mode(new window) because browsers limit access to their web storage in Private mode. We therefore recommend against using this search if you are using Private mode.
- If you sign out of your Proton Mail account, your index will still be available the next time you sign in.
- If you clear your browser data(new window), your index will be erased.
How to search message content
If you haven’t performed a content search before, the app will show you a pop-up asking if you want to search message content. Click Activate.
Confirm that you want to Enable the ability to search your messages’ contents. Once done, your messages will be downloaded from Proton Mail’s servers, decrypted, and indexed locally in an encrypted state.
This process may take a few minutes and can be quite resource-intensive. You can Pause indexing your messages and resume indexing later, and you can still perform a standard search while this indexing is in progress.
If you have searched your message content before but are using a different browser, you will need to create a new index.
Click Advanced search options to add parameters and logic functions when you search your messages’ content.
Performing a search will now return results that include the contents of your messages.
- Your index will be kept up to date automatically — new emails will be added regularly as long as your browser is open.
- If you have not used your browser for some time, the index might need a few seconds to automatically update before you can search message content again.
- If your mailbox is very large, you can speed searches up by disabling Search message content. The index will not be erased if you do this.
Although rare, the contents of a large inbox may be larger than your browser’s web storage capacity. In this case, a date will be displayed showing how far back in time you can search the contents of your encrypted messages.
Because the index size is limited by your browser’s web storage capacity, this date will be updated as new emails arrive in your inbox to ensure recent messages can be searched.
You may see the following error messages:
Content search cannot be enabled in this browser. Please try another browser.
Your browser does not support web storage. Please use one of our recommended browsers(new window) instead.
Please activate your content search again
The index is no longer valid or has become corrupted. You will need to rebuild the index by disabling and then re-enabling the search message content option (see above).