Download APK

The file name downloaded is Tutanota - Encrypted Email & Calendar-375010.apk.

Make sure that third-party apps are allowed on your device. Simply pop over to your phone's Settings menu (usually found by hitting the menu button from the home screen) and tap the option for Applications. You can see an option that says "Unknown Source" Fill the check box next to it, then click OK on the resulting popup alert.

• From the Homescreen go to Settings >> More.
• Go to Security >> Device administration.
• Check "Unknown Source"

That’s it! Android manufactures have added the security settings of "Unknown Source" to prevent the installation of any app other than from Google play store. If this option is enabled, you are allowed to install apps from third party sources. Now you are able to install apps that you downloaded.

How to install multiple APKs (App bundle) as if it was a single package?

Split APKs Installer (SAI) APK is an app that lets you install multiple APKs as if it was a single package. This is useful for installing apps that are distributed as App Bundles since Android provides no built-in way to install them from sources other than Google Play.

How to use SAI?

• Download and Install: Split APKs Installer (SAI) APK
• Download All files APKs of com.aefyr.sai
• Open (SAI) App
• Click Pick APKs button and select all files APKs of Tutanota - Encrypted Email & Calendar then click Select button to start installation process