[Evolution] Misleading GPG error message from Evolution

[Patrick O'Callaghan <poc usb ve>]

Evolution 3.18.5.2
gnupg2-2.1.11-1.fc23.x86_64

(This one cost me several days of fruitless bug-hunting).

I attempted to send an encrypted and signed email to two recipients.
Every time I would get the following error message:

    Could not create message.

    Because "gpg: skipped "XXXXXXXX": No secret key
    gpg: signing failed: No secret key
    ", you may need to select different mail options.

Naturally my focus was on trying to figure out what was wrong with my
secret key (which I had successfully used before, and from Evo). After
a good deal of head-banging I took the radical step of using
Thunderbird with Enigmail, and the problem jumped out immediately: I
didn't have the public key of one of the recipients in my keyring. When
I removed that recipient and tried again, everything worked.

I realise that the error message shown by Evo was produced by gpg (or
gpg2 - I have both but don't know which one it's using). However TBird
managed to get this right and tell what was going on.

What can be done about this?

poc