How to send a message encrypted with an arbitrary PGP key to the recipient?

For the address, it allows you to select only the key with the ID and no other.

K-9 Mail doesn’t support letting you do everything that’s possible using OpenPGP. If you need that kind of control, K-9 Mail is not the right client for you.

It is a pity that K-9 Mail cannot do this. :frowning_face: