Register yourself at the Apples TestFlight program.
You can install Letterbox app when opening TestFlight app on your device.
Use your personal mail account to setup Letterbox and to get access to your mails.
We add a first welcome mail from our mail bot in your inbox. You can chat with our mail bot.
Please answering our online survey about Letterbox and end-to-end communication. You find the link in the welcome mail.
You can use letterbox how ever you like. We are happy to get any feedback from you.
You can stop using Letterbox any time. Letterbox creates a secret (key) on your device and the secret (key) is required to decrypt mails. When you like to read encrypted mails on other devices, you have to export the key to these devices. You find more in our FAQ. Please consider exporting your secret key before removing Letterbox, otherwise you might lose access to encrypted mails.