Add check for public keys of all message recipients (to, cc, and bcc)
before sending the message. Adds an OnFocusLost callback to header
editors to facilitate a callback for checking keys whenever a new
recipient is added (OnChange results in too many keyring checks).
Once encryption is initially set, the callbacks are registered. If a
public key is not available for any recipient, encryption is turned off.
However, notably, the callbacks are still registered meaning as s soon
as the user removes the recipients with missing keys, encryption is
turned back on.
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Tested-by: Koni Marti <koni.marti@gmail.com>
32a16dcd8d