Peter, unfortunately, my Trash department is set to bin things straight away. And I didn't try at all to remove the sponsored message, as I realise that you can't get rid of them. I wasn't touching any of my laptop's keys at the time, so it was a bit disconcerting to see the emails vanish. Oh dear, sometimes I think I'm getting too old for all this technology.
Thank you to all who responded. Hope it doesn't keep happening!