Recommended use is with Thunderbird and Enigmail on desktop, where you should also have your mail filters sorting your mail to the IMAP folders.
To install use F-Droid. F-Droid ist the Open Software Repository for Android. https://f-droid.org/
This is/feels like the recommended way to use PGP at the moment or at least the most useable.
There's an open issue to add PPG/MIME: https://code.google.com/p/k9mail/issues/detail?id=5864
There's also an open bounty which can be contributed to: https://www.bountysource.com/issues/815255-pgp-mime
You can get the latest K9 Alpha from here: https://github.com/k9mail/k-9/releases/tag/4.904
..and should use OpenKeyChain instead of APG, since its no longer maintained. http://openkeychain.org/ (also available on F-Droid)
This at least removes the need to push decrypt on every Message although thee might be Bugs.
Recommended use is with Thunderbird and Enigmail on desktop, where you should also have your mail filters sorting your mail to the IMAP folders.
To install use F-Droid. F-Droid ist the Open Software Repository for Android. https://f-droid.org/
This is/feels like the recommended way to use PGP at the moment or at least the most useable.