Im marking this as Accepted Solution having also reads the newer thread on this.
Ive not decided its not something to be concerned about but will say its pretty poor the way this is configured with BT leaving less knowledgeable customers to work it out via this forum , why they could not have explained in the launch e mail is very poor.
This happens all the time with mine - even ones which I know are secure. Another problem is trying to open messages and they refuse to open (or the one next on the list will open.) Just wish we could go back to the old way. I'd dump BT Mail altogether if it wasn't for the fact so many folk know my BT addresses. Poor show BT.