added fairemail and improved thunderbird pgp

wiki/android/fairemail.md

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+# FairEmail
+
+[FairEmail](https://email.faircode.eu/) is a free and open-source email client for
+[Android](/wiki/android.md).
+
+## Setup
+
+On [Android](/wiki/android.md) FairEmail is available on [F-Droid](/wiki/android/f-droid.md) in a
+package called [FairEmail](https://f-droid.org/en/packages/eu.faircode.email/).
+Additionally it is available on the[Google Play store](/wiki/android.md#app-store) in a package
+called [FairEmail](https://play.google.com/store/apps/details?id=eu.faircode.email&hl=de).
+
+## Usage
+
+This section addresses the usage of FairEmail.
+
+### Use PGP Key for Encryption, Decryption and Signing
+
+FairEmail can use [OpenPGP](/wiki/openpgp.md) to sign, encrypt or decrypt mails.
+To achieve this download [OpenKeychain](https://www.openkeychain.org/).
+To connect FairEmail with OpenKeychain navigate to the settings and select `Encryption`.
+There the provider of OpenPGP (`OpenPGP provider`) can be set to OpenKeychain
+(`org.sufficientlysecure.keychain`).
+Using OpenKeychain PGP keys can then be imported and stored.
+
+After this is done outgoing mails can be encrypted by signed or encrypted by selecting the
+`Encrypt` selection on the top bar when writing emails.
+
+Decryption can be done by clicking on the padlock when inside an email that is encrypted.
+
+Additionally in the settings under `Encryption` the signing (`Sign by default`), encryption
+(`Sign and encrypt by default`), decryption (`Auomatically decrypt messages`) and validation
+(`Automatically verify signed messages`) can be set to occurr automatically.