End-to-end-encrypted mails


Who reads your mails? With regular mails you, the receiver, all mail providers and maybe others can read them. With end-to-end encrypted mails only the sender and the receivers can read them. Our iOS-App Letterbox makes end-to-end encryption easy to use, is compatible with most mail providers and supports the standard encryption protocol OpenPGP.

Letterbox is simlar to common mail apps but indicates the security state of incoming and outgoing mails. We disinguish between a confidential and insecure mails.

Confidential mail

  • Only you and the sender know the content of the mail.
  • You know which mails the sender sent before.
  • Sender and receiver need Letterbox or compatible mail client.

Insecure mail

  • You, the sender and all involed mail providers know the cntent of the mail.
  • But who sent the mail? Sender addresses can be freely chosen.
  • A fraud can impersonate a person when using a known mail address as sender address.

Letterbox is a free open-source mail client on iOS and part of an ongoing research project at the Freie Universität Berlin, Germany. Letterbox is still under development but you can soon use the app on your device with Apple's TestFlight app.

Get Letterbox More information


Letterbox is a result of the research project enzevalos. The goal of the enzevalos project is to investigate means to render electronic mail encryption easy to use by most e-mail users. Letterbox was developted at the Freie Universität Berlin for research purposes and was studied in the lab.

We are grateful to the German Bundesministerium für Bildung und Forschung (BMBF) for funding this project. Projektpartner were Freie Universität Berlin, Technische Universität Berlin und die Wincor-Nixdorf International GmbH. Bitcoin Deutschland AG, Open-Xchange AG, Peering GmbH (ECIX) und Mynigma were associated project partners. The project started in January 2016 and ended in March 2018.

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