One of the more difficult issues for OpenPGP-aware E-Mail clients is the support and treatment of different e-mail formats, i.e. PGP/INLINE, PGP/MIME, and the variants thereof. While developers are usually aware of the quirks of their own implementations, it is difficult to find reliable documentation on the matter without doing extensive research on the clients.
I would like to collect on this page the behavior of different implementations, for both sending and receiving e-mail. It is more important to have a general overview here than a deep understanding of each implementation, so information should be kept to the point. I will make a start, feel free to use the same fields or suggest a better way to structure this information when you add your own.
K-9 Mail + OpenKeychain
Supported receiving formats: PGP/INLINE, encrypted and clearsigned
Preferred receiving format: PGP/INLINE
Supported sending formats: PGP/INLINE
Preferred sending format: PGP/INLINE
Platform limitations and quirks:
The current stable release is based on the original Android Open Source Project E-Mail client, which squashed all mail at receive time into a single html blob to display for performance reasons, irrecoverably losing necessary information for PGP/MIME processing.
Planned development:
Full PGP/MIME support is in the works. The development master has a revised database architecture but is missing a migration mechanism. PGP supported is patched directly into the K-9 code, so there are no technical limitations.
Contact for questions: Vincent Breitmoser <look@my.amazin.horse>