Delta Chat, a chat program that uses e-mail as the transport protocol and supports end to end encryption, is now available in the beta channel of Google Play.
If you are already using an older version, you will have to backup your data, uninstall it, install the new version and import the data.
This worked flawlessly for me
I’m using it with an separate e-mail account which I have created for it, so it does not clutter my existing e-mail, but in theory it should be able to coexist.