Here you can select the key to OpenPGP-encrypt messages to when using this identity and when encrypting emails, always also encrypt to the certificate of my own identity are in effect. This key is also used for the Attach → Attach My Public Key function of the Composer.
To change the selected key, press the Change... button. A dialog listing all OpenPGP keys found in your keyring will be shown allowing you to select the one to use.
You can clear the list of keys and get more information about them in the same way as described for OpenPGP signing key.
