Office 365 Message Encryption Viewer
Office 365 Message Encryption (OME) allows email users to send and receive encrypted messages. With the OME Viewer app, you can view and reply to OME encrypted messages, right from your Android device.
After downloading OME Viewer, open the message in your email app, tap the attachment, and choose 'OME Viewer'.
Requirement: Android 4.0+