Aha!!
Double stupid me.
1) No - that tick box didn't used to exist did it - or it used to be default on. I certainly have messages in my outbox but I have never actively ticked a box for that. Know about it now. Thanks.
2) Ritchie, Russell, tomato tomatoe, ... ok so Russell prob does now have 2 hopefully similar messages from me. Sorry for the confusion. Thanks for working out what I was trying to do.
3) I need to stop posting on forums a) late at night and/or b) while supposed to be working on something else.
As you were, nothing to see here ... move along now ....