Most instant messengers today, including WhatsApp, Signal, Telegram, Threema, Wire and others, support end-to-end encryption (E2EE) of text messages. In fact, messengers that don’t support E2E encryption are usually considered dubious. However, when it comes to e-mails, things are mostly still quite insecure – even in 2020.
The majority of personal- and business-related e-mails are still sent as plain text (however, at least encrypted in transit  mostly). A major reason is the fact that PGP (e.g. with OpenPGP) is still quite cumbersome to set up and use for non-technical people. Morever, PGP has some issues, however, some kind of encryption is usually better than none at all.
If you want to learn more about E2EE for e-mails, I recommend this article by ProtonMail. However, E2EE is not particularly the topic of this post.
While true end-to-end-encrypted communication requires both parties to have a working PGP setup and is therefore impractical to realize without cooperation, you can at least boost your e-mail security to a certain extent by encrypting your own inbox. That is, mails are stored on the server encryptedly and can, at least, not be read by a malicious attacker and – depending on the implementation – potentially not even by your mail provider. In the following, I want to present the setup with which I realized my personal, encrypted inbox.
First of all, I do not host my own mail server (I used to, but maintining such turned out to be almost a full-time job!), but rely on an external provider. In my case, this provider is mailbox.org, which I can absolutely recommend to anyone. It offers an intuitive webmail, a ton of expert-level configuration options, the ability to bring your own domain, German storage locations and a lot more. Also, they claim to care a lot about privacy and the founder, Peer Heinlein, is both the author of a collection of e-mail technology-related literature and an active supporter of open-source and / or creative commons projects like the Wikimedia foundation. Other PGP-capable e-mail providers include ProtonMail and Posteo.
Mailbox.org supports different kinds of PGP-based encryption, one of them being the “mailbox.org Guard”. In essence, this feature provides server-side encryption of everything inside your inbox using customer-provided PGP keys. While server-side encryption still requires you to trust your provider, I consider it a good compromise between security and still having an intuitive, almost seemless user experience.
Apart from the webmail client I use open-source Thunderbird as my desktop e-mail client. In combination with the Enigmail extension, integration with mailbox.org’s PGP encryption is set up almost trivially. More recent version of Thunderbird even have built-in PGP support. Each time I want to access my inbox from Thunderbird, I am prompted to enter my PGP key’s passphrase. You can also save the key to your operating system’s key store, so you don’t have to enter it repeatedly.
The last missing piece is the ability to read mails from my Android phone as well. Setting that up was a little more complicated as most e-mail clients on Android do not include support for encryption – except for the excellent, fully open-source K-9 Mail client. It integrates with OpenKeychain – a general-purpose, open-source PGP provider for Android. The setup involves to import your PGP keys to OpenKeychain and link it to K-9. Afterwards, it works completely seemless as well. Only when your phone was restarted you are requrired to enter your key’s passphrase.
My intension with this article is to present a working, easy-to-use tech stack for inbox encryption, solely based on open-source software to eventually encourage more people to think about using encryption more extensively. Give it a try!