Email Privacy

Email is the hardest common system to make private, and it is worth understanding why before spending effort on it.

The structural problem

Email was designed in 1981 to be a store-and-forward system that any server could relay a message through. Every design decision since has preserved that property, because it is what makes email work. The consequences:

• Arbitrary servers handle plaintext. Your message passes through your provider, your recipient’s provider, and every intermediate relay, in the clear unless each hop happens to use TLS.
• Transport security is opportunistic. TLS between mail servers is not authenticated end to end in the general case, and a downgrade is not detectable by the user.
• Metadata is the product. Envelope data — who sent to whom, when, which servers were involved — is available to every hop and is the part attackers actually use.

What is worth doing

Use a provider you trust for at least one address. This is the highest-value change, because email is the account-recovery path for everything else you own. Migration to a privacy-focused provider is a bigger job than configuring one, but it moves the most consequential copy of your identity somewhere better.

Turn on two-factor authentication and use an app-based code. See two-factor authentication.

Encrypt at rest where the provider supports it, and understand that this protects you from a stolen laptop or an insider with disk access, not from the provider.

Send sensitive messages elsewhere. For a document that must stay between two people, use an encrypted file shared through a link with a password delivered out of band, or use an end-to-end encrypted messenger. See end-to-end encrypted messaging.

Reducing metadata exposure

• Avoid putting anything sensitive in the subject line, which travels further than the body and is frequently logged separately.
• Understand that the recipient list and the message ID are visible to every hop. A Message-ID can carry a domain, a username, and a timestamp.
• Prefer services that do not retain message content after delivery, and check the retention policy rather than the marketing page.
• Remember forwarding. Once a message is forwarded, every previous hop’s assumption about the recipient is void.

A workable configuration

1. One account at a provider you have deliberately chosen; it becomes your recovery root.
2. Two-factor authentication with an authenticator app, plus a hardware key if your provider supports it.
3. Aliases per context if your provider supports them, so a breach of one address does not connect to the others.
4. Encrypted file transfer instead of attachment for anything that matters.
5. An authenticated SPF and DKIM setup, so that your mail is harder to impersonate and harder to spam-filter out of other people’s inboxes.

Sources

• RFC 5321 — the SMTP specification, including the store-and-forward model that constrains everything.
• RFC 3207 — why plain SMTP has no authenticated transport.
• Autocrypt Level 1 — a minimal, auditable standard for opportunistic encryption, designed so that key management is not the hard part.