Self-hosting a mail server with zero-access encryption for all emails, similar to Protonmail
Self-hosting a mail server with zero-access encryption for all emails, similar to Protonmail
I was interested in hosting my own mail server that provides a similar level of privacy for users as Protonmail, ie the server admin cannot read any emails, even those which are not E2EE with PGP. Is there a self-hostable solution to this?
I'm aware the server admin can't read emails that were sent encrypted using the user's PGP key, but most emails I get are automated emails from companies/services/etc without the option to upload a public key to send the user encrypted email. If you're with a service like Protonmail, the server admin still cannot read even these emails.
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I host my own for mspencer dot net, used this 15-ish step walkthrough from linuxbabe dot com. Only maybe three instances of spam in two years, gmail and outlook receive my messages just fine, etc. (Successful spammers were using legitimate services, and those services took action when notified. Greylist delays emails by a few minutes but it’s extremely effective against most spammers because they never come back to retry messages after a few minutes, while legitimate senders will.) I don’t know if I would accept blanket advice against self hosting.
Fundamentally if your mail server can see the addressee, it can see the content. SMTPS encrypts both in the same channel. So at the point where you accept messages and store them in a mailbox, the messages have to be readable.
Encrypting them at rest isn’t something I currently do, but if you’re going to later serve those messages to an email client that expects to receive clear text, your server needs both the keys and the messages. They can be stored in different places.
Most of your needs could be met with full disk encryption on the box hosting Dovecot. If you’re worried about being compelled to decrypt, there’s always the deck of cards trick: The pass phrase for full disk encryption consists of a memorized portion plus the letters and numbers of the top N cards in this deck of cards you keep by the server. If someone were to shuffle that deck of cards, and the server were powered down, the encrypted volume would be impossible to recover.
I’m eager to learn what other Dovecot tricks people can recommend to improve security.
I'm curious - do you use email aliases to help reduce spam or block specific senders more easily? I've found that aliases can make a big difference in managing privacy and limiting unwanted messages. Startmail, for example, offers aliases as a convenient option without the need for self-hosting.
I do, and I agree about their utility. My users and aliases are in OpenLDAP but it’s pretty easy to add new ones.
Separate accounts are preferable if you’re actually going to be responding to messages. I’ve had some embarrassing encounters where I’ve given an alias to a business that I didn’t realize was going to actually use it for real email conversations with a human. By default roundcube web mail lets you hit reply anyway and the reply goes out with your real address, which can lead to confusion.
That's a great point about alias use in roundcube. I can see how it could get confusing if you accidentally reply with your real address. This is where I think alias services that handle that automatically really shine. Have you ever run into other limitations or surprises with self-hosting, like with spam filtering or uptime? I imagine it could be quite time-consuming to keep up with all the configurations and updates, especially if you're aiming to maintain strong privacy protections.
Not really, it’s been pretty effortless. Every couple months I have to make sure my renewed LetsEncrypt certs really got imported, but I don’t think I’ve had to intervene manually for anything in a long time.