Thanks, reinob. Curioser and curioser. I have just sent my email again, to the same address as before plus two others including yours, and this time it did not bounce
Received-SPF: softfail (google.com: domain of transitioning <YOUR ADDRESS> does not designate 176.32.226.65 as permitted sender) client-ip=176.32.226.65; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning <YOUR ADDRESS> does not designate 176.32.226.65 as permitted sender) smtp.mailfrom=<YOUR ADDRESS>