In short. Reading your email over Tor hides your IP address and location from your email provider and from anyone watching your connection. It doesn’t hide from your provider which account is yours or who you write to, and it doesn’t change how your email travels between providers.
What onion email means
Onion services are services, like websites, that can only be reached through the Tor network. Their location and IP address are hidden, and all traffic between you and an onion service is end-to-end encrypted [1]. Their addresses end in .onion, a special-use domain name registered for Tor [2].
When an email provider has an onion address, it usually means you can open its webmail as an onion service. Your email address itself usually stays a regular one, like name@provider, so people outside Tor can still write to you.
What Tor hides
- Your location from the provider. Tor prevents websites and other services from learning your location [3]. Your provider sees a connection from the Tor network, not your IP address.
- Which services you use from people watching your connection. Tor keeps your internet provider, or someone on your Wi-Fi, from seeing what you do online [3], including that you opened your email. They can still see that you are connecting to the Tor network [3].
What it doesn’t hide
- Who you are, once you sign in. If you sign in to a website, it still doesn’t know your location, but it knows who you are [4]. Your provider knows which account is yours and everything it keeps about it.
- How your email travels after it leaves your provider. Tor covers the connection between you and your provider. From there, your message goes to the recipient’s server the way all email does, server to server [5], and the providers on both ends see who wrote to whom and when: what email metadata shows.
- Apps that don’t use Tor. Tor protects only apps that are set up to send their traffic through it [4]. A mail app on your computer connects directly unless you set it up for Tor.
- Details that point to you. Payment details, a recovery address or a phone number on the account can still identify you: what actually gives a person away in email.
- Attachments you open outside Tor Browser. A document such as a DOC or PDF file can load content from the internet when another app opens it, outside Tor, and that reveals your real IP address [4].
- Someone who can watch both ends. Tor doesn’t fully protect against someone able to observe both your connection and your provider’s [3].
How to use email over Tor
- Install Tor Browser only from torproject.org.
- Open your provider’s webmail in Tor Browser: through its onion address, if it has one, or its usual address.
- If the point is not to be linked to the account, don’t give it details that point to you: a personal phone number, a recovery address you use elsewhere, a card in your name.
Questions
Is onion email end-to-end encrypted? The connection between you and an onion service is [1]. The email itself is a different matter: whether its content is encrypted depends on your provider and on end-to-end encryption between you and the recipient. More in What is end-to-end encryption?
Do I need an onion address, or is Tor Browser enough? With Tor Browser, your provider doesn’t learn your location either way [3]. An onion address also keeps the whole connection inside the Tor network and hides where the service is [1].
What’s next
- What actually gives a person away in email
- Email metadata: what it reveals about you
- What is end-to-end encryption?
Sources
- Tor Project: Onion Services, Tor Browser manual. https://support.torproject.org/onionservices/
- RFC 7686: The “.onion” Special-Use Domain Name. IETF, October 2015. https://www.rfc-editor.org/rfc/rfc7686
- Tor Project: What protections does Tor provide? https://support.torproject.org/about/protections/
- Tor Project: Tor Browser best practices. https://support.torproject.org/faq/staying-anonymous/
- RFC 5321: Simple Mail Transfer Protocol. IETF, October 2008. https://www.rfc-editor.org/rfc/rfc5321