You need to have a pair of public / private PGP keys associated to your email address and to have installed the jolla-email-crypto-gnupg package from default Jolla repositories.
- Copy the private one to the phone and import with
gpg2. - In the setting UI, go to your email account page and scroll to the bottom, you should see that you can choose to sign your emails with your key.
- Compose a new email from this account on device, it should ask you your PGP passphrase before sending the email.
- View your sent email with another client and check that the text is properly displayed and that the signature is attached and possibly checked if your public PGP key is available to your client.
For me this procedure is working with my provider (Free in France) and the sent email is properly displayed and checked on various clients. For @rozgwi it’s not the case and the content of the signature is displayed instead of the mail content.