Sometimes the subject line says more than the email itself. “Your test results.” “Interview on Friday.” “Your loan is approved.” The subject and the sender tell you what it’s about before you open it.
What we decided
Who writes to whom, and about what, is part of the email too. So we will store the subject, sender and recipients the way we store the text.
- Your keys will encrypt the text, attachments, subject, sender and recipients of stored emails.
- We will not keep a record of who writes to whom: senders and recipients will be stored encrypted along with the message. What delivery logs will still keep is under What this doesn’t change and in the inventory.
- The search index will be built on your devices. If a copy of it is ever sent to our servers, it will be sent only encrypted with your keys.
In regular email, the server keeps subject lines and addresses in the clear: that’s how it works.
Why it matters
The subject, the addresses and the time of an email are called metadata. They show who you write to, how often and about what, even when the text itself is encrypted. More in Email metadata: what it reveals about you.
What this doesn't change
Encrypting stored email doesn’t hide what happens to it on the way.
- Delivery. At the moment of delivery the server will see who is writing to whom. A court will be able to order us to start recording it and to hand over the last 7 days of logs.
- Incoming and sending logs. For 7 days the log of incoming mail will keep the minute, the domain and a hash of the rest of the address, under a key that will be destroyed after 7 days. The sending log will keep, for 7 days, the minute and pseudonyms instead of the mailbox and the recipient, under a key that will change every day and never be written down: within a day they will show that one mailbox wrote to one address several times, but not who. While the key exists, a hash could be checked against a guess, including our own users’ addresses.
- The queue and the database archive. Mail to an external address will wait in the send queue for up to 48 hours, and the database change archive will keep the exact time messages were written for 24 to 48 hours.
- Email to other providers. Email sent to another provider without PGP will leave unencrypted, so the recipient’s provider will be able to read it. That provider will always see the subject and the addresses.
The other limits are listed under What Methmail won’t be able to do.
What it costs
The server will know little about an email, so your device will search, sort and group emails into conversations by subject, sender and recipients.
- A new device will first download the encrypted headers of your whole mailbox, day by day, and build the index itself, so older emails will turn up in search as they load. By launch it won’t get a ready index from your other devices.
- The web app will build and keep its encrypted index in your browser and erase it when you sign out. The key will be kept in the same browser, so the encryption won’t protect against malware on your device or an extension with access to the site. The browser decides how much space the index gets.
- Rules by sender will run once any of your devices is online, including an open web app tab; until then the email will wait in your Inbox. Server-side rules will work with your devices off, but they will be stored in the clear, and you’ll see a warning.
There are no numbers yet: we’ll show them once we’ve measured.
What stays in the clear
The server will keep a few things in the clear: without them, mail can’t be sorted into folders or synced. For example, message and folder numbers, “read” marks, the message size to the nearest step, the day received without the hour, and the spam verdict. Why each is needed, and for how long, is in the inventory, under “Mail”.
Everything we will keep in the clear will be in the inventory. Its first rows are already printed.