@purism : I understand you based #libremmail on K-9 and one needs to add OpenKeyChain, create a key, send it...
The PEP application was created (from K-9) to automate the key generation and exchanges. It is not perfect because one cannot easily sync the private key with other apps and devices (e.g. a PC running Thunderbird+Enigmail) and there's (or was ?) a bug where attachments from gmail are not displayed.
However wouldn't be better to help debug PEP to make encryption more user friendly ?