So I managed to encrypt the email body with GnuPG public key..
But I don't figure how I can do the same for the title ?! ThunderBird manage it.. any idea how ? asked on Official Thunderbird forum
I'm not entirely sure what you hope to achieve: have a GPG encrypted subject, and have ThunderBird automatically understand that it's encrypted, so it can be automatically decrypted?
Since you're saying you're building software to support this, what are you building? A ThunderBird plugin that can do this? Or just standalone software that you want to make compatible with ThunderBird default way of handling encryption?